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Transcript

cob19537_ch02_105-119.qxd
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Page 105
Precalculus—
CHAPTER CONNECTIONS
More on Functions
CHAPTER OUTLINE
2.1 Analyzing the Graph of a Function 106
2.2 The Toolbox Functions and Transformations 120
2.3 Absolute Value Functions, Equations,
and Inequalities 136
2.4 Basic Rational Functions and Power Functions;
More on the Domain 148
2.5 Piecewise-Defined Function
163
2.6 Variation: The Toolbox Functions in Action 177
Viewing a function in ter ms of an equation, a
table of values, and the r elated graph, often
brings a clear er understanding of the
relationships involved. For example, the power
generated by a wind turbine is often modeled
8v3
by the function P 1v2 ⫽
, wher e P is the
125
power in watts and v is the wind velocity in
miles per hour . While the for mula enables us
to predict the power generated for a given wind
speed, the graph of fers a visual r epresentation
of this r elationship, wher e we note a rapid
growth in power output as the wind speed
increases.
䊳
This application appears as Exer cise 107 in
Section 2.2.
The foundation and study of calculus involves using absolute value inequalities to analyze very small
differences. The Connections to Calculus for Chapter 2 expands on the notation and language used in
Connections this analysis, and explores the need to solve a broad range of equation types.
to Calculus
105
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Precalculus—
2.1
Analyzing the Graph of a Function
LEARNING OBJECTIVES
In this section, we’ll consolidate and refine many of the ideas we’ve encountered
related to functions. When functions and graphs are applied as real-world models, we
create numeric and visual representations that enable an informed response to questions involving maximum efficiency, positive returns, increasing costs, and other relationships that can have a great impact on our lives.
In Section 2.1 you will see
how we can
A. Determine whether a
B.
C.
D.
E.
function is even, odd, or
neither
Determine intervals
where a function is
positive or negative
Determine where a
function is increasing or
decreasing
Identify the maximum and
minimum values of a
function
Locate local maximum
and minimum values
using a graphing
calculator
A. Graphs and Symmetry
While the domain and range of a function will remain dominant themes in our study,
for the moment we turn our attention to other characteristics of a function’s graph.
We begin with the concept of symmetry.
Figure 2.1
Symmetry with Respect to the y-Axis
Consider the graph of f 1x2 x 4x shown in Figure 2.1, where the portion of the graph to the left of the
y-axis appears to be a mirror image of the portion to the
right. A function is symmetric to the y-axis if, given
any point (x, y) on the graph, the point 1x, y2 is also
on the graph. We note that 11, 32 is on the graph, as
is 11, 32, and that 12, 02 is an x-intercept of the
graph, as is (2, 0). Functions that are symmetric with
respect to the y-axis are also known as even functions
and in general we have:
4
2
5
y f(x) x4 4x2
(2.2, ~4)
(2.2, ~4)
(2, 0)
(2, 0)
5
5
x
(1, 3) 5 (1, 3)
Even Functions: y-Axis Symmetry
A function f is an even function if and only if, for each point (x, y) on the graph of f,
the point (x, y) is also on the graph. In function notation
f 1x2 f 1x2
Symmetry can be a great help in graphing new functions, enabling us to plot fewer
points and to complete the graph using properties of symmetry.
EXAMPLE 1
䊳
Graphing an Even Function Using Symmetr y
a. The function g(x) in Figure 2.2 (shown in solid blue) is known to be even.
Draw the complete graph.
2
Figure 2.2
b. Show that h1x2 x3 is an even function using
y
the arbitrary value x k [show h1k2 h1k2 ],
5
then sketch the complete graph using h(0),
g(x)
h(1), h(8), and y-axis symmetry.
Solution
106
(1, 2)
䊳
a. To complete the graph of g (see Figure 2.2)
use the points (4, 1), (2, 3), (1, 2),
and y-axis symmetry to find additional points.
The corresponding ordered pairs are (4, 1),
(2, 3), and (1, 2), which we use to help
draw a “mirror image” of the partial graph
given.
(1, 2)
(4, 1)
(4, 1)
5 x
5
(2, 3)
(2, 3)
5
2–2
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Precalculus—
2–3
107
Section 2.1 Analyzing the Graph of a Function
2
b. To prove that h1x2 x3 is an even function, we
must show h1k2 h1k2 for any constant k.
2
1
After writing x3 as 3x2 4 3 , we have:
h1k2 ⱨ h1k2
2
2 1k2 ⱨ 2 1k2
3
WORTHY OF NOTE
The proof can
also1be demonstrated
2
by writing x 3 as 1x 3 2 2, and you are
asked to complete this proof in
Exercise 69.
2
3
y
5
(8, 4)
first step of proof
3 1k2 4 ⱨ 3 1k2 4
2
1
3
Figure 2.3
1
3
h(x)
(8, 4)
evaluate h (k ) and h(k )
(1, 1)
2
radical form
result: 1k2 2 k2
3 2
3 2
2
k 2
k ✓
(1, 1)
10
(0, 0)
Using h102 0, h112 1, nd h182 a 4 with
y-axis symmetry produces the graph shown in
Figure 2.3.
10
x
5
Now try Exercises 7 through 12
䊳
Symmetry with Respect to the Origin
Another common form of symmetry is known as symmetry to the origin. As the name
implies, the graph is somehow “centered” at (0, 0). This form of symmetry is easy to
see for closed figures with their center at (0, 0), like certain polygons, circles, and
ellipses (these will exhibit both y-axis symmetry and symmetry with respect to the
origin). Note the relation graphed in Figure 2.4 contains the points (3, 3) and (3, 3),
along with (1, 4) and (1, 4). But the function f (x) in Figure 2.5 also contains these
points and is, in the same sense, symmetric to the origin (the paired points are on opposite sides of the x- and y-axes, and a like distance from the origin).
Figure 2.4
Figure 2.5
y
y
5
5
(1, 4)
(1, 4)
(3, 3)
(3, 3)
5
5
x
f(x)
5
5
(3, 3)
(1, 4)
(3, 3)
(1, 4)
5
x
5
Functions symmetric to the origin are known as odd functions and in general
we have:
Odd Functions: Symmetr y About the Origin
A function f is an odd function if and only if, for each point (x, y) on the graph of f,
the point (x, y) is also on the graph. In function notation
f 1x2 f 1x2
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Precalculus—
108
2–4
CHAPTER 2 More on Functions
EXAMPLE 2
䊳
Graphing an Odd Function Using Symmetr y
a. In Figure 2.6, the function g(x) given (shown in solid blue) is known to be odd.
Draw the complete graph.
b. Show that h1x2 x3 4x is an odd function using the arbitrary value x k
[show h1x2 h1x2 ], then sketch the graph using h122 , h112 , h(0), and
odd symmetry.
Solution
䊳
a. To complete the graph of g, use the points (6, 3), (4, 0), and (2, 2) and
odd symmetry to find additional points. The corresponding ordered pairs are
(6, 3), (4, 0), and (2, 2), which we use to help draw a “mirror image” of the
partial graph given (see Figure 2.6).
Figure 2.6
Figure 2.7
y
y
10
5
(1, 3)
g(x)
(6, 3)
(2, 2)
(4, 0)
10
h(x)
(2, 0)
x
(6, 3)
10
(4, 0)
(2, 2)
5
(2, 0)
(0, 0)
5
x
(1, 3)
10
5
b. To prove that h1x2 x3 4x is an odd function, we must show that
h1k2 h1k2.
h1k2 ⱨ h1k2
1k2 41k2 ⱨ 3 k3 4k 4
k3 4k k3 4k ✓
3
Using h122 0, h112 3, and h102 0 with symmetry about the origin
produces the graph shown in Figure 2.7.
Now try Exercises 13 through 24
A. You’ve just seen how
we can determine whether a
function is even, odd, or
neither
䊳
Finally, some relations also exhibit a third form of symmetry, that of symmetry to
the x-axis. If the graph of a circle is centered at the origin, the graph has both odd and
even symmetry, and is also symmetric to the x-axis. Note that if a graph exhibits x-axis
symmetry, it cannot be the graph of a function.
B. Intervals Where a Function Is Positive or Negative
Consider the graph of f 1x2 x2 4 shown in Figure 2.8, which has x-intercepts at
(2, 0) and (2, 0). As in Section 1.5, the x-intercepts have the form (x, 0) and are called
the zeroes of the function (the x-input causes an output of 0). Just as zero on the number line separates negative numbers from positive numbers, the zeroes of a function
that crosses the x-axis separate x-intervals where a function is negative from x-intervals
where the function is positive. Noting that outputs (y-values) are positive in Quadrants I
and II, f 1x2 7 0 in intervals where its graph is above the x-axis. Conversely, f 1x2 6 0
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Precalculus—
2–5
109
Section 2.1 Analyzing the Graph of a Function
in x-intervals where its graph is below the x-axis. To illustrate, compare the graph of f
in Figure 2.8, with that of g in Figure 2.9.
Figure 2.8
5
(2, 0)
Figure 2.9
y f(x) x2 4
5
y g(x) (x 4)2
(2, 0)
5
5
x
3
(4, 0)
x
5
(0, 4)
5
The graph of f is a parabola, with x-intercepts of (2, 0) and (2, 0). Using our previous observations, we note f 1x2 0 for x 1q, 24 ´ 3 2, q2 since the graph is
above the x-axis, and f 1x2 6 0 for x 12, 22 . The graph of g is also a parabola, but
is entirely above or on the x-axis, showing g1x2 0 for x ⺢. The difference is that
zeroes coming from factors of the form (x r) (with degree 1) allow the graph to
cross the x-axis. The zeroes of f came from 1x 22 1x 22 0. Zeroes that come
from factors of the form 1x r2 2 (with degree 2) cause the graph to “bounce” off the
x-axis (intersect without crossing) since all outputs must be nonnegative. The zero of
g came from 1x 42 2 0.
WORTHY OF NOTE
These observations form the basis
for studying polynomials of higher
degree in Chapter 4, where we
extend the idea to factors of the
form 1x r2 n in a study of roots of
multiplicity.
EXAMPLE 3
5
䊳
Solving an Inequality Using a Graph
Use the graph of g1x2 x3 2x2 4x 8 given to solve the inequalities
a. g1x2 0
b. g1x2 6 0
Solution
䊳
From the graph, the zeroes of g (x-intercepts)
occur at (2, 0) and (2, 0).
a. For g1x2 0, the graph must be on or above
the x-axis, meaning the solution is
x 32, q 2 .
b. For g1x2 6 0, the graph must be below the
x-axis, and the solution is x 1q, 22 .
As we might have anticipated from the
graph, factoring by grouping gives
g1x2 1x 22 1x 22 2, with the graph
crossing the x-axis at 2, and bouncing
off the x-axis (intersects without crossing)
at x 2.
y
(0, 8)
g(x)
5
5
5
x
2
Now try Exercises 25 through 28
䊳
Even if the function is not a polynomial, the zeroes can still be used to find
x-intervals where the function is positive or negative.
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Precalculus—
110
2–6
CHAPTER 2 More on Functions
EXAMPLE 4
䊳
Solution
䊳
Solving an Inequality Using a Graph
y
For the graph of r 1x2 1x 1 2 shown, solve
a. r 1x2 0
b. r 1x2 7 0
a. The only zero of r is at (3, 0). The graph is on
or below the x-axis for x 31, 3 4 , so
r 1x2 0 in this interval.
b. The graph is above the x-axis for x 13, q 2 ,
and r 1x2 7 0 in this interval.
10
r(x)
10
10
10
Now try Exercises 29 through 32
B. You’ve just seen how
we can determine intervals
where a function is positive or
negative
x
䊳
This study of inequalities shows how the graphical solutions studied in Section 1.5
are easily extended to the graph of a general function. It also strengthens the foundation for the graphical solutions studied throughout this text.
C. Intervals Where a Function Is Increasing or Decreasing
In our study of linear graphs, we said a graph was increasing if it “rose” when
viewed from left to right. More generally, we say the graph of a function is increasing on a given interval if larger and larger x-values produce larger and larger
y-values. This suggests the following tests for intervals where a function is increasing
or decreasing.
Increasing and Decreasing Functions
Given an interval I that is a subset of the domain, with x1 and x2 in I and x2 7 x1,
1. A function is increasing on I if f 1x2 2 7 f 1x1 2 for all x1 and x2 in I
(larger inputs produce larger outputs).
2. A function is decreasing on I if f 1x2 2 6 f 1x1 2 for all x1 and x2 in I
(larger inputs produce smaller outputs).
3. A function is constant on I if f 1x2 2 f 1x1 2 for all x1 and x2 in I
(larger inputs produce identical outputs).
f(x)
f (x) is increasing on I
f(x2)
f (x)
f (x) is decreasing on I
f(x) is constant on I
f (x)
f (x1)
f(x1)
f (x2)
f (x2)
f (x1)
f (x1)
f (x1)
x1
Interval I
x2
x2 x1 and f (x2) f (x1)
for all x I
graph rises when viewed
from left to right
x
x1
Interval I
x2
x2 x1 and f (x2) f (x1)
for all x I
graph falls when viewed
from left to right
f(x2)
f(x1)
f (x2)
x
x1
Interval I
x2
x
x2 x1 and f(x2) f(x1)
for all x I
graph is level when viewed
from left to right
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Precalculus—
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111
Section 2.1 Analyzing the Graph of a Function
Consider the graph of f 1x2 x2 4x 5
given in Figure 2.10. Since the parabola opens
downward with the vertex at (2, 9), the function
must increase until it reaches this peak at x 2, and
decrease thereafter. Notationally we’ll write this as
f 1x2c for x 1q, 22 and f 1x2T for x 12, q 2.
Using the interval 13, 22 shown below the figure,
we see that any larger input value from the interval
will indeed produce a larger output value, and f 1x2c
on the interval. For instance,
1 7 2
x2 7 x1
and
and
f 112 7 f 122
8 7 7
Figure 2.10
10
y f(x) x2 4x 5
(2, 9)
(0, 5)
(1, 0)
(5, 0)
5
5
x
10
x (3, 2)
f 1x2 2 7 f 1x1 2
A calculator check is shown in the figure. Note the outputs are increasing until x 2,
then they begin decreasing.
EXAMPLE 5
䊳
Finding Intervals Where a Function Is Increasing
or Decreasing
y
5
Use the graph of v(x) given to name the interval(s)
where v is increasing, decreasing, or constant.
Solution
䊳
From left to right, the graph of v increases until
leveling off at (2, 2), then it remains constant
until reaching (1, 2). The graph then increases
once again until reaching a peak at (3, 5) and
decreases thereafter. The result is v1x2c for
x 1q, 22 ´ 11, 32, v1x2T for x 13, q 2, and
v(x) is constant for x 12, 12 .
5
5
Questions about the behavior of a
function are asked with respect to
the y outputs: is the function
positive, is the function increasing,
etc. Due to the input/output,
cause/effect nature of functions,
the response is given in terms of x,
that is, what is causing outputs to
be positive, or to be increasing.
C. You’ve just seen how
we can determine where a
function is increasing or
decreasing
䊳
Notice the graph of f in Figure 2.10 and the graph of v in Example 5 have something in common. It appears that both the far left and far right branches of each graph
point downward (in the negative y-direction). We say that the end-behavior of both
graphs is identical, which is the term used to describe what happens to a graph as 冟x冟 becomes very large. For x 7 0, we say a graph is, “up on the right” or “down on the
right,” depending on the direction the “end” is pointing. For x 6 0, we say the graph
is “up on the left” or “down on the left,” as the case may be.
䊳
Describing the End-Behavior of a Graph
The graph of f 1x2 x 3x is shown. Use the
graph to name intervals where f is increasing or
decreasing, and comment on the end-behavior of
the graph.
y
5
3
Solution
x
5
Now try Exercises 33 through 36
WORTHY OF NOTE
EXAMPLE 6
v(x)
䊳
From the graph we observe that f 1x2c for
x 1q, 12 ´ 11, q 2 , and f 1x2T for x 11, 12 .
The end-behavior of the graph is down on the left,
and up on the right (down/up).
f(x) x2 3x
5
5
x
5
Now try Exercises 37 through 40
䊳
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Precalculus—
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2–8
CHAPTER 2 More on Functions
D. Maximum and Minimum Values
The y-coordinate of the vertex of a parabola that opens downward, and the y-coordinate
of “peaks” from other graphs are called maximum values. A global maximum (also
called an absolute maximum) names the largest y-value over the entire domain. A
local maximum (also called a relative maximum) gives the largest range value in a
specified interval; and an endpoint maximum can occur at an endpoint of the domain.
The same can be said for any corresponding minimum values.
We will soon develop the ability to locate maximum and minimum values for
quadratic and other functions. In future courses, methods are developed to help locate
maximum and minimum values for almost any function. For now, our work will rely
chiefly on a function’s graph.
EXAMPLE 7
䊳
Analyzing Characteristics of a Graph
Analyze the graph of function f shown in
Figure 2.11. Include specific mention of
a. domain and range,
b. intervals where f is increasing or decreasing,
c. maximum (max) and minimum (min) values,
d. intervals where f 1x2 0 and f 1x2 6 0, and
e. whether the function is even, odd, or neither.
Solution
D. You’ve just seen how
we can identify the maximum
and minimum values of a
function
䊳
a. Using vertical and horizontal boundary lines
show the domain is x ⺢, with a range of:
y 1q, 74 .
b. f 1x2c for x 1q, 32 ´ 11, 52 shown
in blue in Figure 2.12, and f 1x2T for
x 13, 12 ´ 15, q 2 as shown in red.
c. From part (b) we find that y 5 at (3, 5) and
y 7 at (5, 7) are local maximums, with a
local minimum of y 1 at (1, 1). The point (5, 7)
is also a global maximum (there is no global
minimum).
d. f 1x2 0 for x 36, 84 ; f 1x2 6 0 for
x 1q, 62 ´ 18, q 2
e. The function is neither even nor odd.
Figure 2.11
y
10
(5, 7)
f(x)
(3, 5)
(1, 1)
10
10
x
10
Figure 2.12
y
10
(5, 7)
(3, 5)
(6, 0)
(1, 1)
10
(8, 0)
10 x
10
Now try Exercises 41 through 48
䊳
E. Locating Maximum and Minimum Values Using Technology
In Section 1.5, we used the 2nd TRACE (CALC) 2:zero option of a graphing calculator to locate the zeroes/x-intercepts of a function. The maximum or minimum values
of a function are located in much the same way. To illustrate, enter the function
y x3 3x 2 as Y1 on the Y= screen, then
Figure 2.13
graph it in the window shown, where x 3 4, 44
5
and y 35, 5 4 . As seen in Figure 2.13, it
appears a local maximum occurs at x 1 and
a local minimum at x 1. To actually find the
local maximum, we access the 2nd TRACE 4
4
(CALC) 4:maximum option, which returns
you to the graph and asks for a Left Bound?, a
Right Bound?, and a Guess? as before. Here,
we entered a left bound of “3,” a right bound
5
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Precalculus—
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113
Section 2.1 Analyzing the Graph of a Function
Figure 2.14
of “0” and bypassed the guess option by pressing
a third time (the calculator again sets
5
the “䉴” and “䉳” markers to show the bounds
chosen). The cursor will then be located at the
local maximum in your selected interval, with
4
the coordinates displayed at the bottom of the 4
screen (Figure 2.14). Due to the algorithm
the calculator uses to find these values, a decimal number very close to the expected value is
5
sometimes displayed, even if the actual value
is an integer (in Figure 2.14, 0.9999997 is
displayed instead of 1). To check, we evaluate f 112 and find the local maximum
is indeed 0.
ENTER
EXAMPLE 8
䊳
Locating Local Maximum and Minimum V alues on a Graphing Calculator
Find the maximum and minimum values of f 1x2 Solution
䊳
1 4
1x 8x2 72 .
2
1 4
1X 8X2 72 as Y1 on the Y= screen, and graph the
2
function in the ZOOM 6:ZStandard window. To locate the leftmost minimum value,
we access the 2nd TRACE (CALC) 3:minimum option, and enter a left bound of
“4,” and a right bound of “1” (Figure 2.15). After pressing
once more, the
cursor is located at the minimum in the interval we selected, and we find that a
local minimum of 4.5 occurs at x 2 (Figure 2.16). Repeating these steps
using the appropriate options shows a local maximum of y 3.5 occurs at x 0,
and a second local minimum of y 4.5 occurs at x 2. Note that y 4.5 is
also a global minimum.
Begin by entering
ENTER
Figure 2.15
Figure 2.16
10
10
10
E. You’ve just seen how
we can locate local maximum
and minimum values using a
graphing calculator
10
10
10
10
10
Now try Exercises 49 through 54
䊳
The ideas presented here can be applied to functions of all kinds, including
rational functions, piecewise-defined functions, step functions, and so on. There is a
wide variety of applications in Exercises 57 through 64.
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Precalculus—
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2–10
CHAPTER 2 More on Functions
2.1 EXERCISES
䊳
CONCEPTS AND VOCABULAR Y
Fill in each blank with the appropriate word or phrase. Carefully reread the section if needed.
1. The graph of a polynomial will cross through the
x-axis at zeroes of
factors of degree 1, and
off the x-axis at the zeroes from linear
factors of degree 2.
3. If f 1x2 2 7 f 1x1 2 for x1 6 x2 for all x in a given
interval, the function is
in the interval.
5. Discuss/Explain the following statement and give
an example of the conclusion it makes. “If a
function f is decreasing to the left of (c, f (c)) and
increasing to the right of (c, f (c)), then f (c) is either
a local or a global minimum.”
䊳
2. If f 1x2 f 1x2 for all x in the domain, we say that
f is an
function and symmetric to the
axis. If f 1x2 f 1x2 , the function is
and symmetric to the
.
4. If f 1c2 f 1x2 for all x in a specified interval, we
say that f (c) is a local
for this interval.
6. Without referring to notes or textbook, list as many
features/attributes as you can that are related to
analyzing the graph of a function. Include details
on how to locate or determine each attribute.
DEVELOPING YOUR SKILLS
The following functions are known to be even. Complete
each graph using symmetry.
7.
8.
y
5
5
5 x
3
15. f 1x2 4 1
xx
1
16. g1x2 x3 6x
2
1
17. p1x2 3x3 5x2 1 18. q1x2 x
x
y
10
10
10 x
Determine whether the following functions are even,
odd, or neither.
10
5
Determine whether the following functions are even:
f 1k2 f 1k2 .
9. f 1x2 7冟 x 冟 3x2 5 10. p1x2 2x4 6x 1
1
11. g1x2 x4 5x2 1
3
1
冟x冟
x2
The following functions are known to be odd. Complete
each graph using symmetry.
13.
12. q1x2 14.
y
10
Determine whether the following functions are odd:
f 1k2 f 1k2 .
19. w1x2 x3 x2
3
20. q1x2 x2 3冟x冟
4
1
3
21. p1x2 2 1 x x3
4
22. g1x2 x3 7x
23. v1x2 x3 3冟x冟
Use the graphs given to solve the inequalities indicated.
Write all answers in interval notation.
25. f 1x2 x3 3x2 x 3; f 1x2 0
y
10
y
5
10
10 x
10
10 x
5
10
24. f 1x2 x4 7x2 30
5 x
10
5
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115
Section 2.1 Analyzing the Graph of a Function
26. f 1x2 x3 2x2 4x 8; f 1x2 7 0
32. g1x2 1x 12 3 1; g1x2 6 0
y
y
5
5
5
5 x
g(x)
5
5 x
1
27. f 1x2 x4 2x2 1; f 1x2 7 0
y
5
5
5 x
5
Name the interval(s) where the following functions are
increasing, decreasing, or constant. Write answers using
interval notation. Assume all endpoints have integer
values.
33. y V1x2
34. y H1x2
y
y
10
5
28. f 1x2 x3 2x2 4x 8; f 1x2 0
y
1
5
10
10 x
5
5 x
H(x)
5
5 x
10
35. y f 1x2
5
5
36. y g1x2
y
y
10
10
3
29. p1x2 1 x 1 1; p1x2 0
y
f(x)
8
g(x)
6
10
5
10 x
4
2
10
5
2
4
6
8
x
10
5 x
p(x)
For Exercises 37 through 40, determine (a) interval(s)
where the function is increasing, decreasing or constant,
and (b) comment on the end-behavior.
5
30. q1x2 1x 1 2; q1x2 7 0
y
37. p1x2 0.51x 22 3
3
38. q1x2 1
x1
y
5
y
5
5
(0, 4)
q(x)
5
5 x
(2, 0)
5
31. f 1x2 1x 12 1; f 1x2 0
3
y
5
(1, 0)
5
5 x
5
5
39. y f 1x2
5 x
(0, 1)
5
40. y g1x2
y
y
10
5
5
f(x)
5 x
10
5
5
10 x
5 x
3
10
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CHAPTER 2 More on Functions
For Exercises 41 through 48, determine the following
(answer in interval notation as appropriate): (a) domain
and range of the function; (b) zeroes of the function;
(c) interval(s) where the function is greater than or
equal to zero, or less than or equal to zero; (d) interval(s)
where the function is increasing, decreasing, or constant;
and (e) location of any local max or min value(s).
42. y f 1x2
41. y H1x2
5
y (2, 5)
45. y Y1
46. y Y2
y
y
5
5
5
5
5 x
5 x
5
5
47. p1x2 1x 32 3 1 48. q1x2 冟x 5冟 3
y
5
y
y
10
10
(1, 0)
(3.5, 0)
(3, 0)
5
5 x
5
8
5 x
6
10
5 (0, 5)
10 x
4
5
2
43. y g1x2
44. y h1x2
10
y
y
5
5 x
g(x)
2
5
x
2
4
6
8
10
x
Use a graphing calculator to find the maximum and
minimum values of the following functions. Round
answers to nearest hundredth when necessary.
5
5
2
5
3 3
6
1x 5x2 6x2 50. y 1x3 4x2 3x2
4
5
51. y 0.0016x5 0.12x3 2x
49. y 52. y 0.01x5 0.03x4 0.25x3 0.75x2
54. y x2 2x 3 2
53. y x 24 x
䊳
WORKING WITH FORMULAS
55. Conic sections—hyperbola: y 13 24x2 36
y
While the conic sections are
5
not covered in detail until
f(x)
later in the course, we’ve
already developed a number
5
5 x
of tools that will help us
understand these relations
and their graphs. The
5
equation here gives the
“upper branches” of a hyperbola, as shown in the
figure. Find the following by analyzing the equation:
(a) the domain and range; (b) the zeroes of the
relation; (c) interval(s) where y is increasing or
decreasing; (d) whether the relation is even, odd, or
neither, and (e) solve for x in terms of y.
56. Trigonometric graphs: y sin1x2 and y cos1x2
The trigonometric functions are also studied at
some future time, but we can apply the same tools
to analyze the graphs of these functions as well.
The graphs of y sin x and y cos x are given,
graphed over the interval x 3360°, 360°4 . Use
them to find (a) the range of the functions;
(b) the zeroes of the functions; (c) interval(s)
where y is increasing/decreasing; (d) location of
minimum/maximum values; and (e) whether
each relation is even, odd, or neither.
y
y
(90, 1)
1
1
y cos x
y sin x
(90, 0)
360 270 180
90
90
1
180
270
360 x
360 270 180
90
90
1
180
270
360 x
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䊳
117
Section 2.1 Analyzing the Graph of a Function
APPLICATIONS
c.
d.
e.
f.
g.
h.
Height (feet)
57. Catapults and projectiles: Catapults have a long
and interesting history that dates back to ancient
times, when they were used to launch javelins,
rocks, and other projectiles. The diagram given
illustrates the path of the projectile after release,
which follows a parabolic arc. Use the graph to
determine the following:
80
70
60
50
40
30
20
60
100
140
180
220
260
Distance (feet)
a. State the domain and range of the projectile.
b. What is the maximum height of the projectile?
c. How far from the catapult did the projectile
reach its maximum height?
d. Did the projectile clear the castle wall, which
was 40 ft high and 210 ft away?
e. On what interval was the height of the
projectile increasing?
f. On what interval was the height of the
projectile decreasing?
P (millions of dollars)
58. Profit and loss: The profit of
DeBartolo Construction Inc.
is illustrated by the graph
shown. Use the graph to
t (years since 1990)
estimate the point(s) or the
interval(s) for which the profit P was:
a. increasing
b. decreasing
16
12
8
4
0
4
8
1 2 3 4 5 6 7 8 9 10
constant
a maximum
a minimum
positive
negative
zero
59. Functions
and rational exponents: The graph of
2
f 1x2 x3 1 is shown. Use the graph to find:
a. domain and range of the function
b. zeroes of the function
c. interval(s) where f 1x2 0 or f 1x2 6 0
d. interval(s) where f (x) is increasing, decreasing,
or constant
e. location of any max or min value(s)
Exercise 59
Exercise 60
y
y
5
5
(1, 0) (1, 0)
5
(0, 1)
5
(3, 0)
5 x
(3, 0)
(0, 1)
5
5 x
5
60. Analyzing a graph: Given h1x2 冟x2 4冟 5,
whose graph is shown, use the graph to find:
a. domain and range of the function
b. zeroes of the function
c. interval(s) where h1x2 0 or h1x2 6 0
d. interval(s) where f(x) is increasing, decreasing,
or constant
e. location of any max or min value(s)
61. Analyzing interest rates: The graph shown approximates the average annual interest rates I on 30-yr fixed mortgages,
rounded to the nearest 14 % . Use the graph to estimate the following (write all answers in interval notation).
a. domain and range
b. interval(s) where I(t) is increasing, decreasing, or constant
c. location of any global maximum or
d. the one-year period with the greatest rate of increase and
minimum values
the one-year period with the greatest rate of decrease
Source: 2009 Statistical Abstract of the United States, Table 1157
16
Mortgage rate
14
12
10
8
6
4
2
0
t
83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09
Year (1983 → 83)
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CHAPTER 2 More on Functions
62. Analyzing the surplus S: The following graph approximates the federal surplus S of the United States. Use the
graph to estimate the following. Write answers in interval notation and estimate all surplus values to the nearest
$10 billion.
a. the domain and range
b. interval(s) where S(t) is increasing, decreasing, or constant
c. the location of any global maximum and minimum values
d. the one-year period with the greatest rate of increase, and the one-year period with the greatest rate of decrease
S(t): Federal Surplus (in billions)
Source: 2009 Statistical Abstract of the United States, Table 451
400
200
0
200
400
600
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108
t
Year (1980 → 80)
64. Constructing a graph: Draw a continuous function
g that has the following characteristics, then state
the zeroes and the location of all maximum and
minimum values. [Hint: Write them as (c, g(c)).]
a. Domain: x 1q, 8 4
Range: y 36, q2
b. g102 4.5; g162 0
c. g1x2c for x 16, 32 ´ 16, 82
g1x2T for x 1q, 62 ´ 13, 62
d. g1x2 0 for x 1q, 94 ´ 33, 8 4
g1x2 6 0 for x 19, 32
63. Constructing a graph: Draw a continuous function
f that has the following characteristics, then state
the zeroes and the location of all maximum and
minimum values. [Hint: Write them as (c, f (c)).]
a. Domain: x 110, q2
Range: y 16, q2
b. f 102 0; f 142 0
c. f 1x2c for x 110, 62 ´ 12, 22 ´ 14, q 2
f 1x2T for x 16, 22 ´ 12, 42
d. f 1x2 0 for x 3 8, 44 ´ 3 0, q 2
f 1x2 6 0 for x 1q, 82 ´ 14, 02
䊳
EXTENDING THE CONCEPT
Exercise 65
65. Does the function shown have a maximum value? Does it have a minimum value?
Discuss/explain/justify why or why not.
y
5
Distance (meters)
66. The graph drawn here depicts a 400-m race between a mother and her daughter. Analyze
the graph to answer questions (a) through (f).
a. Who wins the race, the mother or daughter?
b. By approximately how many meters?
c. By approximately how many seconds?
Exercise 66
Mother
Daughter
d. Who was leading at t 40 seconds?
400
e. During the race, how many seconds was
300
the daughter in the lead?
f. During the race, how many seconds was
200
the mother in the lead?
5
5 x
5
100
10
20
30
40
50
Time (seconds)
60
70
80
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Section 2.1 Analyzing the Graph of a Function
119
67. The graph drawn here depicts the last 75 sec of the competition between Ian Thorpe (Australia) and
Massimiliano Rosolino (Italy) in the men’s 400-m freestyle at the 2000 Olympics, where a new Olympic
record was set.
a. Who was in the lead at 180 sec? 210 sec?
b. In the last 50 m, how many times were they tied, and when did the ties occur?
c. About how many seconds did Rosolino have the lead?
d. Which swimmer won the race?
e. By approximately how many seconds?
f. Use the graph to approximate the new Olympic record set in the year 2000.
Thorpe
Rosolino
Distance (meters)
400
350
300
250
150
155
160
165
170
175
180
185
190
195
200
205
210
215
220
225
Time (seconds)
68. Draw the graph of a general function f (x) that has a
local maximum at (a, f (a)) and a local minimum at
(b, f (b)) but with f 1a2 6 f 1b2 .
䊳
2
69. Verify that h1x2 ⫽ x3 is an even function, by first
rewriting h as h1x2 ⫽ 1x3 2 2.
1
MAINTAINING YOUR SKILLS
70. (Appendix A.4) Solve the given quadratic equation
by factoring: x2 ⫺ 8x ⫺ 20 ⫽ 0.
71. (Appendix A.5) Find the (a) sum and (b) product of the
3
3
rational expressions
and
.
x⫹2
2⫺x
72. (1.4) Write the equation of the line shown, in the
form y ⫽ mx ⫹ b.
73. (Appendix A.2) Find the surface area and volume of the
cylinder shown 1SA ⫽ 2␲r 2 ⫹ ␲r 2h, V ⫽ ␲r 2h2 .
y
36 cm
5
12 cm
⫺5
5 x
⫺5
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Precalculus—
2.2
The Toolbox Functions and Transformations
LEARNING OBJECTIVES
In Section 2.2 you will see
how we can:
A. Identify basic
B.
C.
D.
E.
characteristics of the
toolbox functions
Apply vertical/horizontal
shifts of a basic graph
Apply vertical/horizontal
reflections of a basic
graph
Apply vertical stretches
and compressions of a
basic graph
Apply transformations on
a general function f (x )
Many applications of mathematics require that we select a function known to fit the
context, or build a function model from the information supplied. So far we’ve looked
at linear functions. Here we’ll introduce the absolute value, squaring, square root,
cubing, and cube root functions. Together these are the six toolbox functions, so called
because they give us a variety of “tools” to model the real world (see Section 2.6). In the
same way a study of arithmetic depends heavily on the multiplication table, a study of
algebra and mathematical modeling depends (in large part) on a solid working knowledge of these functions. More will be said about each function in later sections.
A. The Toolbox Functions
While we can accurately graph a line using only two points, most functions require
more points to show all of the graph’s important features. However, our work is greatly
simplified in that each function belongs to a function family, in which all graphs from
a given family share the characteristics of one basic graph, called the parent function.
This means the number of points required for graphing will quickly decrease as we
start anticipating what the graph of a given function should look like. The parent functions and their identifying characteristics are summarized here.
The Toolbox Functions
Identity function
Absolute value function
y
y
5
x
f(x) x
3
3
2
2
1
1
0
0
0
1
1
1
1
2
2
2
2
3
3
3
3
x
f (x) x
3
3
2
2
1
1
0
f(x) x
5
5
x
5
5
Square root function
y
y
5
f (x) 1x
f(x) x2
x
3
9
2
2
4
1
1
1
0
0
0
0
1
1
1
1
2
1.41
2
4
3
1.73
9
4
2
x
3
120
x
Domain: x (q, q), Range: y [0, q)
Symmetry: even
Decreasing: x (q, 0); Increasing: x (0, q )
End-behavior: up on the left/up on the right
Vertex at (0, 0)
Domain: x (q, q), Range: y (q, q)
Symmetry: odd
Increasing: x (q, q)
End-behavior: down on the left/up on the right
Squaring function
5
5
x
Domain: x (q, q), Range: y [0, q)
Symmetry: even
Decreasing: x (q, 0); Increasing: x (0, q)
End-behavior: up on the left/up on the right
Vertex at (0, 0)
5
5
x
Domain: x [0, q), Range: y [0, q)
Symmetry: neither even nor odd
Increasing: x (0, q)
End-behavior: up on the right
Initial point at (0, 0)
2–16
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121
Section 2.2 The Toolbox Functions and Transformations
Cubing function
Cube root function
y
y
10
x
f (x) 1 x
27
27
3
2
8
8
2
1
1
1
1
0
0
0
0
1
1
1
1
2
8
8
2
3
27
27
3
x
f (x) x
3
3
5
x
5
3
f(x) 3 x
10
10
x
5
Domain: x (q, q), Range: y (q, q)
Symmetry: odd
Increasing: x (q, q)
End-behavior: down on the left/up on the right
Point of inflection at (0, 0)
Domain: x (q, q), Range: y (q, q)
Symmetry: odd
Increasing: x (q, q)
End-behavior: down on the left/up on the right
Point of inflection at (0, 0)
In applications of the toolbox functions, the parent graph may be “morphed”
and/or shifted from its original position, yet the graph will still retain its basic shape
and features. The result is called a transformation of the parent graph.
EXAMPLE 1
Solution
䊳
䊳
Identifying the Characteristics of a T ransformed Graph
The graph of f 1x2 x2 2x 3 is given.
Use the graph to identify each of the features
or characteristics indicated.
a. function family
b. domain and range
c. vertex
d. max or min value(s)
e. intervals where f is increasing or decreasing
f. end-behavior
g. x- and y-intercept(s)
a.
b.
c.
d.
e.
f.
g.
y
5
5
5
x
5
The graph is a parabola, from the squaring function family.
domain: x 1q, q 2 ; range: y 3 4, q 2
vertex: (1, 4)
minimum value y 4 at (1, 4)
decreasing: x 1q, 12, increasing: x 11, q 2
end-behavior: up/up
y-intercept: (0, 3); x-intercepts: (1, 0) and (3, 0)
Now try Exercises 7 through 34
A. You’ve just seen how
we can identify basic
characteristics of the
toolbox functions
䊳
Note that for Example 1(f), we can algebraically verify the x-intercepts by substituting 0 for f(x) and solving the equation by factoring. This gives 0 1x 121x 32 ,
with solutions x 1 and x 3. It’s also worth noting that while the parabola is no
longer symmetric to the y-axis, it is symmetric to the vertical line x 1. This line is
called the axis of symmetry for the parabola, and for a vertical parabola, it will always
be a vertical line that goes through the vertex.
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2–18
CHAPTER 2 More on Functions
B. Vertical and Horizontal Shifts
As we study specific transformations of a graph, try to develop a global view as the
transformations can be applied to any function. When these are applied to the toolbox
functions, we rely on characteristic features of the parent function to assist in completing the transformed graph.
Vertical Translations
We’ll first investigate vertical translations or vertical shifts of the toolbox functions,
using the absolute value function to illustrate.
EXAMPLE 2
䊳
Graphing Vertical Translations
Solution
䊳
A table of values for all three functions is given, with the corresponding graphs
shown in the figure.
Construct a table of values for f 1x2 x, g1x2 x 1, and h1x2 x 3 and
graph the functions on the same coordinate grid. Then discuss what you observe.
x
f (x) x g(x) x 1
h(x) x 3
3
3
4
0
2
2
3
1
1
1
2
2
0
0
1
3
1
1
2
2
2
2
3
1
3
3
4
0
(3, 4)5
y g(x) x 1
(3, 3)
(3, 0)
1
f(x) x
5
5
x
h(x) x 3
5
Note that outputs of g(x) are one more than the outputs of f (x), and that each point
on the graph of f has been shifted upward 1 unit to form the graph of g. Similarly,
each point on the graph of f has been shifted downward 3 units to form the graph of
h, since h1x2 f 1x2 3.
Now try Exercises 35 through 42
䊳
We describe the transformations in Example 2 as a vertical shift or vertical translation of a basic graph. The graph of g is the graph of f shifted up 1 unit, and the graph
of h, is the graph of f shifted down 3 units. In general, we have the following:
Vertical Translations of a Basic Graph
Given k 7 0 and any function whose graph is determined by y f 1x2 ,
1. The graph of y f 1x2 k is the graph of f(x) shifted upward k units.
2. The graph of y f 1x2 k is the graph of f(x) shifted downward k units.
Graphing calculators are wonderful tools for
exploring graphical transformations. To emphasize
that a given graph is being shifted vertically as in
3
Example 2, try entering 1
X as Y1 on the Y= screen,
then Y2 Y1 2 and Y3 Y1 3 (Figure 2.17 —
recall the Y-variables are accessed using VARS
(Y-VARS)
). Using the Y-variables in this way enables us to study identical transformations on a variety
of graphs, simply by changing the function in Y1.
ENTER
Figure 2.17
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123
Section 2.2 The Toolbox Functions and Transformations
Using a window size of x 35, 54 and
y 3 5, 54 for the cube root function, produces the graphs shown in Figure 2.18, which
demonstrate the cube root graph has been
shifted upward 2 units (Y2), and downward
3 units (Y3).
Try this exploration again using
Y1 1X.
Figure 2.18
5
Y2
5
5
Y3
5
Horizontal Translations
The graph of a parent function can also be shifted left or right. This happens when we
alter the inputs to the basic function, as opposed to adding or subtracting something to
the function itself. For Y1 x2 2 note that we first square inputs, then add 2,
which results in a vertical shift. For Y2 1x 22 2, we add 2 to x prior to squaring
and since the input values are affected, we might anticipate the graph will shift along
the x-axis — horizontally.
EXAMPLE 3
䊳
Graphing Horizontal Translations
Solution
䊳
Both f and g belong to the quadratic family and their graphs are parabolas. A table
of values is shown along with the corresponding graphs.
Construct a table of values for f 1x2 x2 and g1x2 1x 22 2, then graph the
functions on the same grid and discuss what you observe.
x
f (x) x2
y
g(x) (x 2)2
3
9
1
2
4
0
1
1
1
0
0
4
1
1
9
2
4
16
3
9
25
9
8
(3, 9)
(1, 9)
7
f(x) x2
6
5
(0, 4)
4
(2, 4)
3
g(x) (x 2)2
2
1
5 4 3 2 1
1
1
2
3
4
5
x
It is apparent the graphs of g and f are identical, but the graph of g has been shifted
horizontally 2 units left.
Now try Exercises 43 through 46
䊳
We describe the transformation in Example 3 as a horizontal shift or horizontal
translation of a basic graph. The graph of g is the graph of f, shifted 2 units to the left.
Once again it seems reasonable that since input values were altered, the shift must be
horizontal rather than vertical. From this example, we also learn the direction of the
shift is opposite the sign: y 1x 22 2 is 2 units to the left of y x2. Although it may
seem counterintuitive, the shift opposite the sign can be “seen” by locating the new
x-intercept, which in this case is also the vertex. Substituting 0 for y gives
0 1x 22 2 with x 2, as shown in the graph. In general, we have
Horizontal Translations of a Basic Graph
Given h 7 0 and any function whose graph is determined by y f 1x2 ,
1. The graph of y f 1x h2 is the graph of f(x) shifted to the left h units.
2. The graph of y f 1x h2 is the graph of f(x) shifted to the right h units.
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2–20
CHAPTER 2 More on Functions
Figure 2.19
To explore horizontal translations on a
graphing calculator, we input a basic function in
Y1 and indicate how we want the inputs altered
in Y2 and Y3. Here we’ll enter X3 as Y1 on the
Y=
screen, then Y2 Y1 1X 52 and
Y3 Y1 1X 72 (Figure 2.19). Note how this 10
duplicates the definition and notation for horizontal shifts in the orange box. Based on what
we saw in Example 3, we expect the graph of
y x3 will first be shifted 5 units left (Y2), then
7 units right (Y3). This in confirmed in Figure 2.20.
Try this exploration again using Y1 abs1X2.
Figure 2.20
Y3
10
10
10
EXAMPLE 4
䊳
Graphing Horizontal Translations
Sketch the graphs of g1x2 x 2 and h1x2 1x 3 using a horizontal shift of
the parent function and a few characteristic points (not a table of values).
Solution
䊳
The graph of g1x2 x 2 (Figure 2.21) is the absolute value function shifted
2 units to the right (shift the vertex and two other points from y x 2 . The graph
of h1x2 1x 3 (Figure 2.22) is a square root function, shifted 3 units to the left
(shift the initial point and one or two points from y 1x).
Figure 2.21
5
Figure 2.22
y g(x) x 2
y h(x) x 3
(1, 3)
5
(6, 3)
(5, 3)
(1, 2)
5
Vertex
(2, 0)
5
x
4
B. You’ve just seen how
we can perform vertical/
horizontal shifts of a basic
graph
(3, 0)
5
x
Now try Exercises 47 through 50
䊳
C. Vertical and Horizontal Reflections
The next transformation we investigate is called a vertical reflection, in which we
compare the function Y1 f 1x2 with the negative of the function: Y2 f 1x2 .
Vertical Reflections
EXAMPLE 5
䊳
Graphing Vertical Reflection
Construct a table of values for Y1 x2 and Y2 x2, then graph the functions on
the same grid and discuss what you observe.
Solution
䊳
A table of values is given for both functions, along with the corresponding graphs.
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Section 2.2 The Toolbox Functions and Transformations
y
5
x
Y1 x2
Y2 x2
2
4
4
1
1
1
0
0
0
1
1
1
2
4
4
Y1 x2
(2, 4)
5 4 3 2 1
Y2 x2
1
2
3
4
5
x
(2, 4)
5
As you might have anticipated, the outputs for f and g differ only in sign. Each
output is a reflection of the other, being an equal distance from the x-axis but on
opposite sides.
Now try Exercises 51 and 52
䊳
The vertical reflection in Example 5 is called a reflection across the x-axis.
In general,
Vertical Reflections of a Basic Grap
For any function y f 1x2 , the graph of y f 1x2
is the graph of f(x) reflected across the x-axis.
To view vertical reflections on a graphing calculator, we simply define Y2 Y1, as seen here
3
using 1 X as Y1 (Figure 2.23). As in Section 1.5,
we can have the calculator graph Y2 using a
bolder line, to easily distinguish between the
original graph and its reflection (Figure 2.24). To
aid in the viewing, we have set a window size of
x 35, 5 4 and y 3 3, 34 .
Try this exploration again using Y1 X2 4.
Figure 2.23
Figure 2.24
3
5
5
3
Horizontal Reflections
It’s also possible for a graph to be reflected horizontally across the y-axis. Just as we
noted that f(x) versus f 1x2 resulted in a vertical reflection, f(x) versus f 1x2 results in
a horizontal reflection.
EXAMPLE 6
䊳
Graphing a Horizontal Reflectio
Solution
䊳
A table of values is given here, along with the corresponding graphs.
Construct a table of values for f 1x2 1x and g1x2 1x, then graph the
functions on the same coordinate grid and discuss what you observe.
x
f(x) 1x
g(x) 1x
4
not real
2
2
not real
12 1.41
1
not real
1
0
0
0
1
1
not real
2
12 1.41
not real
4
2
not real
y
(4, 2)
(4, 2)
2
g(x) x
f(x) x
1
5 4 3 2 1
1
2
1
2
3
4
5
x
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The graph of g is the same as the graph of f, but it has been reflected across the
y-axis. A study of the domain shows why — f represents a real number only for
nonnegative inputs, so its graph occurs to the right of the y-axis, while g represents
a real number for nonpositive inputs, so its graph occurs to the left.
Now try Exercises 53 and 54
䊳
The transformation in Example 6 is called a horizontal reflection of a basic
graph. In general,
Horizontal Reflections of a Basic Grap
For any function y f 1x2 , the graph of y f 1x2
is the graph of f(x) reflected across the y-axis.
C. You’ve just seen how we
can apply vertical/horizontal
reflections of a basic graph
D. Vertically Stretching/Compressing a Basic Graph
As the words “stretching” and “compressing” imply, the graph of a basic function can
also become elongated or flattened after certain transformations are applied. However,
even these transformations preserve the key characteristics of the graph.
EXAMPLE 7
䊳
Stretching and Compressing a Basic Graph
Solution
䊳
A table of values is given for all three functions, along with the corresponding
graphs.
Construct a table of values for f 1x2 x2, g1x2 3x2, and h1x2 13x2, then graph
the functions on the same grid and discuss what you observe.
x
f (x) x2
g(x) 3x2
h(x) 13 x2
3
9
27
3
2
4
12
4
3
1
1
3
1
3
0
0
0
0
1
1
3
1
3
2
4
12
4
3
3
9
27
3
y g(x) 3x2
(2, 12)
(2, 4)
f(x) x2
10
h(x) ax2
(2, d)
5 4 3 2 1
1
2
3
4
5
x
4
The outputs of g are triple those of f, making these outputs farther from the x-axis
and stretching g upward (making the graph more narrow). The outputs of h are
one-third those of f, and the graph of h is compressed downward, with its outputs
closer to the x-axis (making the graph wider).
WORTHY OF NOTE
In a study of trigonometry, you’ll
find that a basic graph can also
be stretched or compressed
horizontally, a phenomenon known
as frequency variations.
Now try Exercises 55 through 62
䊳
The transformations in Example 7 are called vertical stretches or compressions
of a basic graph. Notice that while the outputs are increased or decreased by a constant
factor (making the graph appear more narrow or more wide), the domain of the function remains unchanged. In general,
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Section 2.2 The Toolbox Functions and Transformations
Stretches and Compressions of a Basic Graph
For any function y f 1x2 , the graph of y af 1x2 is
1. the graph of f(x) stretched vertically if a 7 1,
2. the graph of f(x) compressed vertically if 0 6 a 6 1.
Figure 2.25
Figure 2.26
To use a graphing calculator in a study of
stretches and compressions, we simply define Y2
and Y3 as constant multiples of Y1 (Figure 2.25).
As seen in Example 7, if a 7 1 the graph will be
stretched vertically, if 0 6 a 6 1, the graph will
be vertically compressed. This is further illus- 0
trated here using Y1 1X, with Y2 2Y1 and
Y3 0.5Y1. Since the domain of y 1x is restricted to nonnegative values, a window size of
x 30, 10 4 and y 3 1, 74 was used (Figure 2.26).
Try this exploration again using Y1 abs1X2 4.
D. You’ve just seen how we
can apply vertical stretches and
compressions of a basic graph
7
10
1
E. Transformations of a General Function
If more than one transformation is applied to a basic graph, it’s helpful to use the following sequence for graphing the new function.
General Transformations of a Basic Graph
Given a function y f 1x2 , the graph of y af 1x h2 k can be obtained by
applying the following sequence of transformations:
1. horizontal shifts 2. reflections 3. stretches/compressions 4. vertical shifts
We generally use a few characteristic points to track the transformations involved,
then draw the transformed graph through the new location of these points.
EXAMPLE 8
Graphing Functions Using Transformations
䊳
Use transformations of a parent function to sketch the graphs of
3
a. g1x2 1x 22 2 3
b. h1x2 2 1
x21
Solution
a. The graph of g is a parabola, shifted left 2 units, reflected across the x-axis, and shifted up 3 units.
This sequence of transformations is shown in Figures 2.27 through 2.29. Note that since the
graph has been shifted 2 units left and 3 units up, the vertex of the parabola has likewise shifted
from (0, 0) to 12, 32 .
䊳
Figure 2.27
y (x Figure 2.28
y
2)2
(4, 4)
5
y x2
5
Figure 2.29
y y (x 2)2
5
y g(x) ⫽ ⫺(x ⫹ 2)2 ⫹ 3
(⫺2, 3)
(0, 4)
(2, 0)
5
(2, 0)
Vertex
5
Shifted left 2 units
5
x
5
5
x
⫺5
(⫺4, ⫺1)
(4, 4)
5
(0, 4)
Reflected across the x-axis
(0, ⫺1)
⫺5
Shifted up 3 units
5
x
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CHAPTER 2 More on Functions
b. The graph of h is a cube root function, shifted right 2, stretched by a factor of 2, then shifted
down 1. This sequence is shown in Figures 2.30 through 2.32 and illustrate how the inflection
point has shifted from (0, 0) to 12, 12 .
Figure 2.30
y
5
Figure 2.31
3
y x 2
5
Figure 2.32
3
y y 2x
2
5
3
y h(x) 2x
21
(3, 2)
(3, 1)
(2, 0)
6 x
Inflection
(1, 1)
4
(2, 0)
6
x
4
(2, 1)
(1, 2)
6
x
(1, 3)
5
5
5
Shifted right 2
(3, 1)
4
Shifted down 1
Stretched by a factor of 2
Now try Exercises 63 through 92
䊳
It’s important to note that the transformations can actually be applied to any
function, even those that are new and unfamiliar. Consider the following pattern:
Parent Function
Transformation of Parent Function
y 21x 32 2 1
quadratic: y x2
absolute value: y 0 x 0
y 2 0 x 3 0 1
3
y 21
x31
cube root: y 1x
3
general: y f 1x2
y 2f 1x 32 1
In each case, the transformation involves a horizontal shift 3 units right, a vertical
reflection, a vertical stretch, and a vertical shift up 1. Since the shifts are the same
regardless of the initial function, we can generalize the results to any function f(x).
WORTHY OF NOTE
Since the shape of the initial graph
does not change when translations
or reflections are applied, these are
called rigid transformations.
Stretches and compressions of a
basic graph are called nonrigid
transformations, as the graph is
distended in some way.
vertical reflections,
vertical stretches and compressions
S
y af 1x h2 k
S
y f 1x2
Transformed Function
S
General Function
horizontal shift
h units, opposite
direction of sign
vertical shift
k units, same
direction as sign
Also bear in mind that the graph will be reflected across the y-axis (horizontally)
if x is replaced with x. This process is illustrated in Example 9 for selected transformations. Remember — if the graph of a function is shifted, the individual points
on the graph are likewise shifted.
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Section 2.2 The Toolbox Functions and Transformations
EXAMPLE 9
䊳
Graphing Transformations of a General Function
Solution
䊳
For g, the graph of f is (1) shifted horizontally 1 unit left (Figure 2.34),
(2) reflected across the x-axis (Figure 2.35), and (3) shifted vertically 2 units down
(Figure 2.36). The final result is that in Figure 2.36.
Given the graph of f(x) shown in Figure 2.33, graph g1x2 f 1x 12 2.
Figure 2.34
Figure 2.33
y
y
5
5
(2, 3)
(3, 3)
f (x)
(0, 0)
5
5
x
5
(1, 0)
(2, 3)
5
x
5
x
(1, 3)
5
5
Figure 2.36
Figure 2.35
y
y
5
5
(1, 3)
(1, 1)
g (x)
(1, 0)
5
5
x
5
(3, 2)
(1, 2)
(5, 2)
(3, 3)
5
(3, 5)
5
Now try Exercises 93 through 96
䊳
As noted in Example 9, these shifts and transformation are often combined—
particularly when the toolbox functions are used as real-world models (Section 2.6).
On a graphing calculator we again define Y1 as needed, then define Y2 as any desired
combination of shifts, stretches, and/or reflections. For Y1 X2, we’ll define Y2 as
2 Y1 1X 52 3 (Figure 2.37), and expect that the graph of Y2 will be that of Y1
shifted left 5 units, reflected across the x-axis, stretched vertically, and shifted up
three units. This shows the new vertex should be at 15, 32 , which is confirmed in
Figure 2.38 along with the other transformations.
Figure 2.38
Figure 2.37
10
10
10
10
Try this exploration again using Y1 abs1X2 .
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Using the general equation y af 1x h2 k, we can identify the vertex, initial
point, or inflection point of any toolbox function and sketch its graph. Given the graph
of a toolbox function, we can likewise identify these points and reconstruct its equation. We first identify the function family and the location (h, k) of any characteristic
point. By selecting one other point (x, y) on the graph, we then use the general equation as a formula (substituting h, k, and the x- and y-values of the second point) to solve
for a and complete the equation.
EXAMPLE 10
䊳
Writing the Equation of a Function Given Its Graph
Find the equation of the function f(x) shown in the figure.
Solution
䊳
The function f belongs to the absolute value family. The
vertex (h, k) is at (1, 2). For an additional point, choose
the x-intercept (3, 0) and work as follows:
y ax h k
0 a 132 1 2
E. You’ve just seen how
we can apply transformations
on a general function f(x)
0 4a 2
2 4a
1
a
2
general equation (function is
shifted right and up)
substitute 1 for h and 2 for k,
substitute 3 for x and 0 for y
simplify
y
5
f(x)
5
5
x
subtract 2
5
solve for a
The equation for f is y 12 0 x 1 0 2.
Now try Exercises 97 through 102
䊳
2.2 EXERCISES
䊳
CONCEPTS AND VOCABULAR Y
Fill in each blank with the appropriate word or phrase. Carefully reread the section if needed.
1. After a vertical
, points on the graph are
farther from the x-axis. After a vertical
,
points on the graph are closer to the x-axis.
3. The vertex of h1x2 31x 52 2 9 is at
and the graph opens
.
5. Given the graph of a general function f (x), discuss/
explain how the graph of F1x2 2f 1x 12 3
can be obtained. If (0, 5), (6, 7), and 19, 42 are
on the graph of f, where do they end up on the
graph of F?
2. Transformations that change only the location of a
graph and not its shape or form, include
and
.
4. The inflection point of f 1x2 21x 42 3 11 is
at
and the end-behavior is
,
.
6. Discuss/Explain why the shift of f 1x2 x2 3 is a
vertical shift of 3 units in the positive direction, while
the shift of g1x2 1x 32 2 is a horizontal shift
3 units in the negative direction. Include several
examples along with a table of values for each.
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䊳
131
Section 2.2 The Toolbox Functions and Transformations
DEVELOPING YOUR SKILLS
By carefully inspecting each graph given, (a) identify the
function family; (b) describe or identify the end-behavior,
vertex, intervals where the function is increasing or
decreasing, maximum or minimum value(s) and x- and
y-intercepts; and (c) determine the domain and range.
Assume required features have integer values.
7. f 1x2 x2 4x
15. r 1x2 314 x 3 16. f 1x2 21x 1 4
y
y
5
5
⫺5
5 x
8. g1x2 x2 2x
y
⫺5
⫺5
⫺5
y
5 x
f(x)
r(x)
5
5
17. g1x2 2 14 x
18. h1x2 21x 1 4
y
⫺5
5 x
⫺5
y
5
5
5 x
g(x)
h(x)
⫺5
⫺5
9. p1x2 x2 2x 3
⫺5
5 x
⫺5
5 x
10. q1x2 x2 2x 8
y
⫺5
⫺5
y
10
5
⫺5
5 x
⫺10
10 x
⫺10
⫺5
11. f 1x2 x2 4x 5
12. g1x2 x2 6x 5
y
For each graph given, (a) identify the function family;
(b) describe or identify the end-behavior, vertex,
intervals where the function is increasing or decreasing,
maximum or minimum value(s) and x- and y-intercepts;
and (c) determine the domain and range. Assume
required features have integer values.
19. p1x2 2x 1 4
y
5
10
10
20. q1x2 3x 2 3
y
y
5
q(x)
⫺10
10 x
⫺10
10 x
⫺5
For each graph given, (a) identify the function family;
(b) describe or identify the end-behavior, initial point,
intervals where the function is increasing or decreasing,
and x- and y-intercepts; and (c) determine the domain
and range. Assume required features have integer values.
13. p1x2 2 1x 4 2
5 x
⫺5
⫺5
⫺10
⫺10
p(x)
5 x
⫺5
21. r 1x2 2x 1 6 22. f 1x2 3x 2 6
y
y
4
6
r(x)
⫺5
⫺5
5 x
5 x
f(x)
14. q1x2 2 1x 4 2
⫺6
⫺4
y
y
5
5
23. g1x2 3x 6
p(x)
24. h1x2 2x 1
y
y
6
6
⫺5
5 x
⫺5
5 x
q(x)
g(x)
⫺5
h(x)
⫺5
⫺5
5 x
⫺4
⫺5
5 x
⫺4
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CHAPTER 2 More on Functions
For each graph given, (a) identify the function family;
(b) describe or identify the end-behavior, inflection
point, and x- and y-intercepts; and (c) determine the
domain and range. Assume required features have
integer values. Be sure to note the scaling of each axis.
25. f 1x2 1x 12 3
26. g1x2 1x 12 3
y
5
f(x)
⫺5
5 x
5 x
27. h1x2 x3 1
3
28. p1x2 2x 1
y
⫺5
5 x
5 x
⫺5
29. q1x2 2x 1 1
3
30. r 1x2 2x 1 1
3
y
y
⫺5
⫺5
5 x
q(x)
⫺5
5 x
r(x)
y
5
32.
f(x)
42. t1x2 0 x 0 3
g1x2 1x 4
45. Y1 0 x 0 , Y2 0 x 4 0
H1x2 1x 42 3
Sketch each graph by hand using transformations of a
parent function (without a table of values).
47. p1x2 1x 32 2
48. q1x2 1x 1
51. g1x2 0 x 0
52. j1x2 1x
3
53. f 1x2 2
x
3
50. f 1x2 1
x2
54. g1x2 1x2 3
Use a graphing calculator to graph the functions given
in the same window. Comment on what you observe.
⫺5
For Exercises 31–34, identify and state the characteristic
features of each graph, including (as applicable) the
function family, end-behavior, vertex, axis of symmetry,
point of inflection, initial point, maximum and minimum
value(s), x- and y-intercepts, and the domain and range.
31.
40. g1x2 1x 4
q1x2 1x 52 2
49. h1x2 x 3
5
5
q1x2 x2 7, r 1x2 x2 3
Use a graphing calculator to graph the functions given
in the same window. Comment on what you observe.
46. h1x2 x3,
⫺5
3
3
g1x2 2
x 3, h1x2 2
x4
39. f 1x2 x3 2
44. f 1x2 1x,
p(x)
h(x)
⫺5
h1x2 1x 3
37. p1x2 x, q1x2 x 5, r 1x2 x 2
43. p1x2 x2,
y
5
5
3
36. f 1x2 2
x,
41. h1x2 x2 3
⫺5
⫺5
g1x2 1x 2,
Sketch each graph by hand using transformations of a
parent function (without a table of values).
g(x)
⫺5
35. f 1x2 1x,
38. p1x2 x2,
y
5
Use a graphing calculator to graph the functions given
in the same window. Comment on what you observe.
y
5
55. p1x2 x2,
q1x2 3x2, r 1x2 15x2
56. f 1x2 1x, g1x2 4 1x,
h1x2 14 1x
57. Y1 0 x 0 , Y2 3 0 x 0 , Y3 13 0 x 0
58. u1x2 x3,
v1x2 8x3,
w1x2 15x3
g(x)
Sketch each graph by hand using transformations of a
parent function (without a table of values).
⫺5
⫺5
5 x
5 x
3
59. f 1x2 4 2
x
61. p1x2 13x3
y
5
⫺5
34.
f(x)
5 x
⫺5
62. q1x2 34 1x
⫺5
⫺5
33.
60. g1x2 2 0x 0
y
5
⫺5
Use the characteristics of each function family to match
a given function to its corresponding graph. The graphs
are not scaled — make your selection based on a careful
comparison.
g(x)
5 x
⫺5
63. f 1x2 12x3
64. f 1x2 2
3 x 2
3
65. f 1x2 1x 32 2 2 66. f 1x2 1
x11
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Section 2.2 The Toolbox Functions and Transformations
67. f 1x2 x 4 1
68. f 1x2 1x 6
71. f 1x2 1x 42 2 3
72. f 1x2 x 2 5
Graph each function using shifts of a parent function
and a few characteristic points. Clearly state and indicate
the transformations used and identify the location of all
vertices, initial points, and/or inflection points.
69. f 1x2 1x 6 1 70. f 1x2 x 1
73. f 1x2 1x 3 1
y
a.
74. f 1x2 1x 32 2 5
y
b.
x
x
75. f 1x2 1x 2 1
76. g1x2 1x 3 2
79. p1x2 1x 32 3 1
80. q1x2 1x 22 3 1
83. f 1x2 x 3 2
84. g1x2 x 4 2
77. h1x2 1x 32 2 2 78. H1x2 1x 22 2 5
3
81. s1x2 1
x12
3
82. t1x2 1
x31
85. h1x2 21x 12 2 3 86. H1x2 12x 2 3
c.
d.
y
3
87. p1x2 13 1x 22 3 1 88. q1x2 41
x12
y
89. u1x2 2 1x 1 3 90. v1x2 3 1x 2 1
x
x
91. h1x2 15 1x 32 2 1
92. H1x2 2x 3 4
Apply the transformations indicated for the graph of the
general functions given.
e.
f.
y
93.
y
y
5
94.
f(x)
y
5
g(x)
(⫺1, 4)
(⫺4, 4)
(3, 2)
(⫺1, 2)
x
x
⫺5
⫺5
5 x
5 x
(⫺4, ⫺2)
⫺5
⫺5
g.
h.
y
y
a. f 1x 22
b. f 1x2 3
c. 12 f 1x 12
d. f 1x2 1
x
x
95.
i.
y
j.
y
5
(2, ⫺2)
a.
b.
c.
d.
96.
h(x)
g1x2 2
g1x2 3
2g1x 12
1
2 g1x 12 2
y
5
y
(⫺1, 3)
(2, 0)
(⫺1, 0)
⫺5
x
5 x
⫺5
y
l.
x
⫺5
y
x
a.
b.
c.
d.
(1, ⫺3)
(2, ⫺4)
h1x2 3
h1x 22
h1x 22 1
1
4 h1x2 5
5 x
(⫺2, 0)
x
(⫺4, ⫺4)
k.
H(x)
⫺5
a.
b.
c.
d.
H1x 32
H1x2 1
2H1x 32
1
3 H1x 22 1
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2–30
CHAPTER 2 More on Functions
Use the graph given and the points indicated to determine the equation of the function shown using the general form
y af(x h) k.
97.
98.
y
5
99.
y
(⫺5, 6)
y
5
(6, 4.5)
5
p(x)
g(x)
(2, 0)
⫺5
5 x
f(x)
⫺5
5 x
⫺3(⫺3, 0)
(0, ⫺4)
⫺5
100.
⫺4
⫺3
(0, ⫺4)
101.
y
(⫺4, 5) 5
x
5
102.
y
5
y
(3, 7)
7
(1, 4)
f(x)
h(x)
r(x)
⫺4
5
x
⫺8
(5, ⫺1)
⫺5
䊳
⫺3
⫺5
7 x
⫺3
(0, ⫺2)
WORKING WITH FORMULAS
103. Volume of a sphere: V(r) 43␲r3
The volume of a sphere is given by the function
shown, where V(r) is the volume in cubic units and
r is the radius. Note this function belongs to the
cubic family of functions. (a) Approximate the
value of 43␲ to one decimal place, then graph the
function on the interval [0, 3]. (b) From your
graph, estimate the volume of a sphere with radius
2.5 in., then compute the actual volume. Are the
results close? (c) For V 43 ␲r3, solve for r in terms
of V.
䊳
2 x
(⫺4, 0)
104. Fluid motion: V(h) 4 1h 20
Suppose the velocity of a fluid flowing from an
open tank (no top) through an opening in its side is
given by the function shown, where V(h) is the
velocity of the fluid (in feet per second) at water
height h (in feet). Note this function belongs to the
square root family of functions. An open tank is
25 ft deep and filled to the brim with fluid. (a) Use
a table of values to graph the
25 ft
function on the interval [0, 25].
(b) From your graph, estimate the
velocity of the fluid when the
water level is 7 ft, then find the
actual velocity. Are the answers
close? (c) If the fluid velocity is
5 ft/sec, how high is the water in the tank?
APPLICATIONS
105. Gravity, distance, time: After being released, the
time it takes an object to fall x ft is given by the
function T1x2 14 1x, where T(x) is in seconds.
(a) Describe the transformation applied to obtain
the graph of T from the graph of y 1x, then
sketch the graph of T for x 3 0, 100 4 . (b) How
long would it take an object to hit the ground if it
were dropped from a height of 81 ft?
106. Stopping distance: In certain weather conditions,
accident investigators will use the function
v1x2 4.91x to estimate the speed of a car (in
miles per hour) that has been involved in an
accident, based on the length of the skid marks x
(in feet). (a) Describe the transformation applied to
obtain the graph of v from the graph of y 1x,
then sketch the graph of v for x 3 0, 4004. (b) If the
skid marks were 225 ft long, how fast was the car
traveling? Is this point on your graph?
107. Wind power: The power P generated by a certain
8 3
v
wind turbine is given by the function P1v2 125
where P(v) is the power in watts at wind velocity v
(in miles per hour). (a) Describe the transformation
applied to obtain the graph of P from the graph of
y v3, then sketch the graph of P for v 3 0, 254
(scale the axes appropriately). (b) How much
power is being generated when the wind is blowing
at 15 mph?
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Section 2.2 The Toolbox Functions and Transformations
108. Wind power: If the power P (in watts) being
generated by a wind turbine is known, the velocity
of the wind can be determined using the function
3
v1P2 52 2
P. (a) Describe the transformation
applied to obtain the graph of v from the graph of
3
y 2
P, then sketch the graph of v for P 3 0, 512 4
(scale the axes appropriately). (b) How fast is the
wind blowing if 343W of power is being generated?
Is this point on your graph?
109. Distance rolled due to gravity: The distance a ball
rolls down an inclined plane is given by the function
d1t2 2t2, where d(t) represents the distance
in feet after t sec. (a) Describe the transformation
applied to obtain the graph of d from the graph
䊳
of y t2, then sketch the graph of d for
t 30, 3 4. (b) How far has the ball rolled after
2.5 sec?
110. Acceleration due to gravity: The velocity of a steel
ball bearing as it rolls down an inclined plane is
given by the function v1t2 4t, where v(t)
represents the velocity in feet per second after t sec.
(a) Describe the transformation applied to obtain
the graph of v from the graph of y t, then sketch
the graph of v for t 30, 34 . (b) What is the velocity
of the ball bearing after 2.5 sec? Is this point on
your graph?
EXTENDING THE CONCEPT
111. Carefully graph the functions f 1x2 x and
g1x2 2 1x on the same coordinate grid. From the
graph, in what interval is the graph of g(x) above
the graph of f(x)? Pick a number (call it h) from this
interval and substitute it in both functions. Is
g1h2 7 f 1h2? In what interval is the graph of g(x)
below the graph of f(x)? Pick a number from this
interval (call it k) and substitute it in both functions.
Is g1k2 6 f 1k2?
䊳
135
112. Sketch the graph of f 1x2 2x 3 8 using
transformations of the parent function, then
determine the area of the region in quadrant I that
is beneath the graph and bounded by the vertical
lines x 0 and x 6.
113. Sketch the graph of f 1x2 x2 4, then sketch the
graph of F1x2 x2 4 using your intuition and
the meaning of absolute value (not a table of
values). What happens to the graph?
MAINTAINING YOUR SKILLS
114. (1.1) Find the distance between the points 113, 92
and 17, 122, and the slope of the line containing
these points.
2x2 3x
5x 2
115. (Appendix A.2) Find
the perimeter of the
figure shown.
5x
2x2 3x 5
1
1
7
2
116. (1.5) Solve for x: x x .
3
4
2
12
117. (2.1) Without graphing, state intervals where f 1x2c
and f 1x2T for f 1x2 1x 42 2 3.
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Precalculus—
2.3
Absolute Value Functions, Equations, and Inequalities
LEARNING OBJECTIVES
While the equations x 1 5 and 冟x 1冟 5 are similar in many respects, note the
first has only the solution x 4, while either x 4 or x 6 will satisfy the second.
The fact there are two solutions shouldn’t surprise us, as it’s a natural result of how
absolute value is defined.
In Section 2.3 you will see
how we can:
A. Solve absolute value
equations
A. Solving Absolute Value Equations
B. Solve “less than”
absolute value
inequalities
C. Solve “greater than”
absolute value
inequalities
D. Solve absolute value
equations and
inequalities graphically
E. Solve applications
involving absolute value
The absolute value of a number x can be thought of as its distance from zero on the number line, regardless of direction. This means 冟x冟 4 will have two solutions, since there
are two numbers that are four units from zero: x 4 and x 4 (see Figure 2.39).
Exactly 4 units
from zero
Figure 2.39
⫺5 ⫺4
Exactly 4 units
from zero
⫺3 ⫺2 ⫺1
0
1
2
3
4
5
This basic idea can be extended to include situations where the quantity within
absolute value bars is an algebraic expression, and suggests the following property.
Property of Absolute Value Equations
WORTHY OF NOTE
If X represents an algebraic expression and k is a positive real number,
Note if k 6 0, the equation 冟X冟 k
has no solutions since the absolute
value of any quantity is always
positive or zero. On a related note,
we can verify that if k 0, the
equation 冟X冟 0 has only the
solution X 0.
then 冟X冟 k
implies X k or X k
As the statement of this property suggests, it can only be applied after the absolute
value expression has been isolated on one side.
EXAMPLE 1
䊳
Solving an Absolute Value Equation
Solve: 5冟x 7冟 2 13.
Solution
䊳
Begin by isolating the absolute value expression.
5冟x 7冟 2 13 original equation
5冟x 7冟 15 subtract 2
冟x 7冟 3
divide by 5 (simplified form)
Now consider x 7 as the variable expression “X” in the property of absolute
value equations, giving
or
x 7 3
x 7 3 apply the property of absolute value equations
x4
or
x 10 add 7
Substituting into the original equation verifies the solution set is {4, 10}.
Now try Exercises 7 through 18
CAUTION
136
䊳
䊳
For equations like those in Example 1, be careful not to treat the absolute value bars as
simple grouping symbols. The equation 51x 72 2 13 has only the solution
x 10, and “misses” the second solution since it yields x 7 3 in simplified form.
The equation 5冟x 7冟 2 13 simplifies to 冟x 7冟 3 and there are actually two
solutions. Also note that 5冟x 7冟 冟5x 35冟!
2–32
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137
Section 2.3 Absolute Value Functions, Equations, and Inequalities
If an equation has more than one solution as in Example 1, they cannot be
simultaneously stored using the, X,T,␪,n key to perform a calculator check (in function or “Func” mode, this is the variable X). While there are other ways to “get
around” this (using Y 1 on the home screen, using a TABLE in ASK mode,
enclosing the solutions in braces as in {4, 10}, etc.), we can also store solutions
using the ALPHA keys. To illustrate, we’ll place the solution x 4 in storage location A,
using 4 STO ALPHA MATH (A). Using this “ STO ALPHA ” sequence we’ll next place the
solution x 10 in storage location B (Figure 2.40). We can then check both solutions
in turn. Note that after we check the first solution, we can recall the expression
using 2nd
and simply change the A to B (Figure 2.41).
ENTER
Figure 2.40
Figure 2.41
Absolute value equations come in many different forms. Always begin by isolating the absolute value expression, then apply the property of absolute value equations to solve.
EXAMPLE 2
䊳
Solving an Absolute Value Equation
Solve:
Solution
䊳
2
` 5 x ` 9 8.
3
2
`5 x ` 9 8
3
2
` 5 x ` 17
3
2
5 x 17
3
2
x 22
3
x 33
Check
WORTHY OF NOTE
As illustrated in both Examples
1 and 2, the property we use to
solve absolute value equations can
only be applied after the absolute
value term has been isolated. As
you will see, the same is true for the
properties used to solve absolute
value inequalities.
䊳
2
For x 33: ` 5 1332 `
3
| 5 21112 |
05 22 0
0 17 0
17
original equation
add 9
or
or
or
98
98
98
98
98
8 8✓
2
5 x 17
3
2
x 12
3
x 18
apply the property of absolute
value equations
subtract 5
multiply by 32
2
1182 `
3
|5 2162 |
0 5 12 0
0 17 0
17
For x 18: ` 5 Both solutions check. The solution set is 518, 336.
98
98
98
98
98
8 8✓
Now try Exercises 19 through 22
䊳
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CHAPTER 2 More on Functions
For some equations, it’s helpful to apply the multiplicative property of absolute
value:
Multiplicative Property of Absolute Value
If A and B represent algebraic expressions,
then 冟AB冟 冟A冟冟B冟.
Note that if A 1 the property says 冟1 # B冟 冟1冟 冟B冟 冟B冟. More generally
the property is applied where A is any constant.
EXAMPLE 3
䊳
Solution
䊳
Solving Equations Using the Multiplicative Proper ty of Absolute Value
Solve: 冟2x冟 5 13.
冟2x冟 5 13
冟2x冟 8
冟2冟冟x冟 8
2冟x冟 8
冟x冟 4
x 4 or x 4
original equation
subtract 5
apply multiplicative property of absolute value
simplify
divide by 2
apply property of absolute value equations
Both solutions check. The solution set is 54, 46.
Now try Exercises 23 and 24
䊳
In some instances, we have one absolute value quantity equal to another, as in 冟A冟 冟B冟.
From this equation, four possible solutions are immediately apparent:
(1) A B
(2) A B
(3) A B
(4) A B
However, basic properties of equality show that equations (1) and (4) are equivalent, as
are equations (2) and (3), meaning all solutions can be found using only equations (1)
and (2).
EXAMPLE 4
䊳
Solving Absolute Value Equations with Two Absolute Value Expressions
Solve the equation 冟2x 7冟 冟x 1冟.
Solution
䊳
This equation has the form 冟A冟 冟B冟, where A 2x 7 and B x 1. From our
previous discussion, all solutions can be found using A B and A B.
AB
2x 7 x 1
2x x 8
x 8
solution template
substitute
subtract 7
subtract x
A B
2x 7 1x 12
2x 7 x 1
3x 6
x 2
solution template
substitute
distribute
add x, subtract 7
divide by 3
The solutions are x 8 and x 2. Verify the solutions by substituting them
into the original equation.
A. You’ve just seen how
we can solve absolute value
equations
Now try Exercises 25 and 26
䊳
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Section 2.3 Absolute Value Functions, Equations, and Inequalities
139
B. Solving “Less Than” Absolute Value Inequalities
Absolute value inequalities can be solved using the basic concept underlying the
property of absolute value equalities. Whereas the equation 冟x冟 4 asks for all numbers
x whose distance from zero is equal to 4, the inequality 冟x冟 6 4 asks for all numbers x
whose distance from zero is less than 4.
Distance from zero is less than 4
Figure 2.42
)
⫺5 ⫺4
⫺3 ⫺2 ⫺1
)
0
1
2
3
4
5
As Figure 2.42 illustrates, the solutions are x 7 4 and x 6 4, which can be written
as the joint inequality 4 6 x 6 4. This idea can likewise be extended to include
the absolute value of an algebraic expression X as follows.
Property I: Absolute Value Inequalities (Less Than)
If X represents an algebraic expression and k is a positive real number,
then 冟X冟 6 k
implies k 6 X 6 k
Property I can also be applied when the “” symbol is used. Also notice that if
k 6 0, the solution is the empty set since the absolute value of any quantity is always
positive or zero.
EXAMPLE 5
Solution
䊳
䊳
Solving “Less Than” Absolute Value Inequalities
Solve the inequalities:
冟3x 2冟
a.
1
4
冟3x 2冟
a.
1
4
冟3x 2冟 4
4 3x 2 4
6 3x 2
2
2 x 3
b. 冟2x 7冟 6 5
original inequality
multiply by 4
apply Property I
subtract 2 from all three parts
divide all three parts by 3
The solution interval is 3 2, 23 4.
b. 冟2x 7冟 6 5
original inequality
Since the absolute value of any quantity is always positive or zero, the solution
for this inequality is the empty set: { }.
Now try Exercises 27 through 38
䊳
As with the inequalities from Section 1.5, solutions to absolute value inequalities
can be checked using a test value. For Example 5(a), substituting x 0 from the
solution interval yields:
1
1✓
2
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2–36
CHAPTER 2 More on Functions
In addition to checking absolute value inequalities using a test value, the TABLE
feature of a graphing calculator can be used, alone or in conjunction with a relational
test. Relational tests have the calculator return a “1” if a given statement is true, and a
“0” otherwise. To illustrate, consider the inequality 2冟x 3冟 1 5. Enter the
expression on the left as Y1, recalling the “abs(” notation is accessed in the MATH menu:
MATH
(NUM) “1:abs(”
(note this option gives only the left parenthesis, you must
supply the right). We can then simply inspect the Y1 column of the TABLE to find outputs that are less than or equal to 5. To use a relational test, we enter Y1 5 as Y2
(Figure 2.43), with the “less than or equal to” symbol accessed using 2nd MATH 6:ⱕ.
Now the calculator will automatically check the truth of the statement for any value of x
(but note we are only checking integer values), and display the result in the Y2 column
of the TABLE (Figure 2.44). After scrolling through the table, both approaches
show that 2冟x 3冟 1 5 for x 僆 [1, 5].
ENTER
Figure 2.43
Figure 2.44
B. You’ve just seen how
we can solve “less than”
absolute value inequalities
C. Solving “Greater Than” Absolute Value Inequalities
For “greater than” inequalities, consider 冟x冟 7 4. Now we’re asked to find all numbers
x whose distance from zero is greater than 4. As Figure 2.45 shows, solutions are
found in the interval to the left of 4, or to the right of 4. The fact the intervals are
disjoint (disconnected) is reflected in this graph, in the inequalities x 6 4 or x 7 4,
as well as the interval notation x 僆 1q, 42 ´ 14, q 2.
Distance from zero
is greater than 4
Figure 2.45
)
⫺7 ⫺6 ⫺5 ⫺4 ⫺3 ⫺2 ⫺1
Distance from zero
is greater than 4
)
0
1
2
3
4
5
6
7
As before, we can extend this idea to include algebraic expressions, as follows:
Property II: Absolute Value Inequalities (Greater Than)
If X represents an algebraic expression and k is a positive real number,
then 冟X冟 7 k
implies X 6 k or X 7 k
EXAMPLE 6
䊳
Solving “Greater Than” Absolute Value Inequalities
Solve the inequalities:
1
x
a. ` 3 ` 6 2
3
2
b. 冟5x 2冟 3
2
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Section 2.3 Absolute Value Functions, Equations, and Inequalities
Solution
䊳
141
a. Note the exercise is given as a less than inequality, but as we multiply both
sides by 3, we must reverse the inequality symbol.
x
1
` 3 ` 6 2
3
2
x
`3 ` 7 6
2
x
x
or 3 7 6
3 6 6
2
2
x
x
6 9
or
7 3
2
2
or
x 7 6
x 6 18
original inequality
multiply by ⴚ3, reverse the symbol
apply Property II
subtract 3
multiply by 2
Property II yields the disjoint intervals x 僆 1q, 182 ´ 16, q2 as the solution.
)
⫺30 ⫺24 ⫺18 ⫺12 ⫺6
)
0
6
12
18
24
30
3
original inequality
2
Since the absolute value of any quantity is always positive or zero, the solution
for this inequality is all real numbers: x 僆 ⺢.
b. 冟5x 2冟 Now try Exercises 39 through 54
䊳
A calculator check is shown for part (a) in Figures 2.46 through 2.48.
Figure 2.46
Figure 2.47
Figure 2.48
This helps to verify the solution interval is x 僆 1q, 182 ´ 16, q 2 .
Due to the nature of absolute value functions, there are times when an absolute
value relation cannot be satisfied. For instance the equation 冟x 4冟 2 has no solutions, as the left-hand expression will always represent a nonnegative value. The inequality 冟2x 3冟 6 1 has no solutions for the same reason. On the other hand, the
inequality 冟9 x冟 0 is true for all real numbers, since any value substituted for x will
result in a nonnegative value. We can generalize many of these special cases as follows.
C. You’ve just seen how
we can solve “greater than”
absolute value inequalities
Absolute Value Functions — Special Cases
Given k is a positive real number and A represents an algebraic expression,
冟A冟 k
冟A冟 6 k
冟A冟 7 k
has no solutions
has no solutions
is true for all
real numbers
See Exercises 51 through 54.
CAUTION
䊳
Be sure you note the difference between the individual solutions of an absolute value
equation, and the solution intervals that often result from solving absolute value inequalities. The solution 52, 56 indicates that both x 2 and x 5 are solutions, while the solution 32, 52 indicates that all numbers between 2 and 5, including 2, are solutions.
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Precalculus—
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2–38
CHAPTER 2 More on Functions
D. Solving Absolute Value Equations
and Inequalities Graphically
The concepts studied in Section 1.5 (solving linear equations and inequalities
graphically) are easily extended to other kinds of relations. Essentially, we treat
each expression forming the equation or inequality as a separate function, then graph
both functions to find points of intersection (equations) or where one graph is above or
Figure 2.49
Figure 2.50
3.1
4.7
3.1
4.7
4.7
3.1
4.7
3.1
below the other (inequalities). For 2冟x 1冟 3 6 2, enter the expression
2冟X 1冟 3 as Y1 on the Y= screen, and 2 as Y2. Using ZOOM 4:ZDecimal
produces the graph shown in Figure 2.49. Using 2nd TRACE (CALC) 5:intersect, we
find the graphs intersect at x 1.5 and x 3.5 (Figure 2.50), and the graph of Y1 is
above the graph of Y2 in this interval. Since this is a “less than” inequality, the solutions
are outside of this interval, which gives x 僆 1q, 1.52 ´ 13.5, q2 as the solution
interval. Note that the zeroes/x-intercept method could also have been used.
EXAMPLE 7
Solution
䊳
Solving Absolute Equations and Inequalities Graphically
1
For f 1x2 2.5冟x 2冟 8 and g1x2 x 3, solve
2
a. f 1x2 g1x2
b. f 1x2 g1x2
c. f 1x2 7 g1x2
䊳
a. With f 1x2 2.5冟x 2冟 8 as Y1 and
1
g1x2 x 3 as Y2 (set to graph in bold),
2
using 2nd TRACE (CALC) 5:intersect
10
shows the graphs intersect 1Y1 Y2 2 at
x 0 and x 5 (see figure). These are
1
the solutions to 2.5冟x 2冟 8 x 3.
2
10
10
10
b. The graph of Y1 is below the graph of Y2 1Y1 6 Y2 2 between these points of
1
intersection, so the solution interval for 2.5冟x 2冟 8 x 3 is x 僆 [0, 5].
2
c. The graph of Y1 is above the graph of Y2 1Y1 7 Y2 2 outside this interval,
1
giving a solution of x 僆 1q, 02 ´ 15, q 2 for 2.5冟x 2冟 8 7 x 3.
2
D. You’ve just seen how
we can solve absolute value
equations and inequalities
graphically
Now try Exercises 55 through 58
䊳
E. Applications Involving Absolute Value
Applications of absolute value often involve finding a range of values for which a given
statement is true. Many times, the equation or inequality used must be modeled after
a given description or from given information, as in Example 8.
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Section 2.3 Absolute Value Functions, Equations, and Inequalities
EXAMPLE 8
䊳
143
Solving Applications Involving Absolute Value Inequalities
For new cars, the number of miles per gallon (mpg) a car will get is heavily
dependent on whether it is used mainly for short trips and city driving, or primarily
on the highway for longer trips. For a certain car, the number of miles per gallon
that a driver can expect varies by no more than 6.5 mpg above or below its field
tested average of 28.4 mpg. What range of mileage values can a driver expect
for this car?
Solution
䊳
Field tested average: 28.4 mpg
mileage varies by no more than 6.5 mpg
⫺6.5
gather information
highlight key phrases
⫹6.5
28.4
make the problem visual
Let m represent the miles per gallon a driver can expect.
Then the difference between m and 28.4 can be no more
than 6.5, or 冟m 28.4冟 6.5.
冟m 28.4冟 6.5
6.5 m 28.4 6.5
21.9 m 34.9
assign a variable
write an equation model
equation model
apply Property I
add 28.4 to all three parts
The mileage that a driver can expect ranges from a low of 21.9 mpg
to a high of 34.9 mpg.
E. You’ve just seen how
we can solve applications
involving absolute value
Now try Exercises 61 through 70
䊳
2.3 EXERCISES
䊳
CONCEPTS AND VOCABULAR Y
Fill in the blank with the appropriate word or phrase. Carefully reread the section if needed.
1. When multiplying or dividing by a negative
quantity, we
the inequality symbol to
maintain a true statement.
2. To write an absolute value equation or inequality in
simplified form, we
the absolute value
expression on one side.
3. The absolute value equation 冟2x 3冟 7 is true
when 2x 3 or when 2x 3 .
4. The absolute value inequality 冟3x 6冟 6 12 is
true when 3x 6 7
and 3x 6 6
Describe the solution set for each inequality (assume k > 0). Justify your answer.
5. 冟ax b冟 6 k
6. 冟ax b冟 7 k
.
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䊳
2–40
CHAPTER 2 More on Functions
DEVELOPING YOUR SKILLS
Solve each absolute value equation. Write the solution in
set notation. For Exercises 7 to 18, verify solutions by
substituting into the original equation. For Exercises
19–26 verify solutions using a calculator.
7. 2冟m 1冟 7 3
8. 3冟n 5冟 14 2
9. 3冟x 5冟 6 15
10. 2冟y 3冟 4 14
11. 2冟4v 5冟 6.5 10.3
12. 7冟2w 5冟 6.3 11.2
13. 冟7p 3冟 6 5
14. 冟3q 4冟 3 5
15. 2冟b冟 3 4
16. 3冟c冟 5 6
17. 2冟3x冟 17 5
18. 5冟2y冟 14 6
19. 3 `
w
4 ` 1 4
2
20. 2 ` 3 v
` 1 5
3
21. 8.7冟p 7.5冟 26.6 8.2
35.
冟5v 1冟
8 6 9
4
36.
冟3w 2冟
6 6 8
2
37. `
1
7
4x 5
` 3
2
6
38. `
2y 3
3
15
` 4
8
16
39. 冟n 3冟 7 7
40. 冟m 1冟 7 5
41. 2冟w冟 5 11
42. 5冟v冟 3 23
43.
44.
冟q冟
2
冟p冟
5
5
1
6
3
3
9
2
4
45. 3冟5 7d冟 9 15
46. 5冟2c 7冟 1 11
47. 2 6 ` 3m 1
4
` 5
5
3
5
2n ` 4
4
22. 5.3冟q 9.2冟 6.7 43.8
48. 4 `
23. 8.7冟2.5x冟 26.6 8.2
49. 4冟5 2h冟 9 7 11
24. 5.3冟1.25n冟 6.7 43.8
50. 3冟7 2k冟 11 7 10
25. 冟x 2冟 冟3x 4冟
51. 3.9冟4q 5冟 8.7 22.5
26. 冟2x 1冟 冟x 3冟
52. 0.9冟2p 7冟 16.11 10.89
Solve each absolute value inequality. Write solutions in
interval notation. Check solutions by back substitution,
or using a calculator.
27. 3冟p 4冟 5 6 8
28. 5冟q 2冟 7 8
29. 3 冟m冟 2 7 4
30. 2冟n冟 3 7 7
31. 冟3b 11冟 6 9
32. 冟2c 3冟 5 6 1
33. 冟4 3z冟 12 6 7
34. 冟2 3u冟 5 4
53. 冟4z 9冟 6 4
54. 冟5u 3冟 8 7 6
Use the intersect command on a graphing calculator
and the given functions to solve (a) f 1x2 g1x2 ,
(b) f 1x2 g1x2 , and (c) f 1x2 6 g1x2 .
55. f 1x2 冟x 3冟 2, g1x2 12x 2
56. f 1x2 冟x 2冟 1, g1x2 32x 9
57. f 1x2 0.5冟x 3冟 1, g1x2 2冟x 1冟 5
58. f 1x2 2冟x 3冟 2, g1x2 冟x 4冟 6
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䊳
Section 2.3 Absolute Value Functions, Equations, and Inequalities
WORKING WITH FORMULAS
59. Spring Oscillation: 冟d x冟 L
A weight attached to a spring hangs at rest a distance
of x in. off the ground. If the weight is pulled down
(stretched) a distance of L inches and released, the
weight begins to bounce and its distance d off the
ground must satisfy the indicated formula. (a) If x
equals 4 ft and the spring is stretched 3 in. and
released, solve the inequality to find what distances
from the ground the weight will oscillate between.
(b) Solve for x in terms of L and d.
䊳
145
60. A “Fair” Coin: `
h 50
` 6 1.645
5
If we flipped a coin 100 times, we expect “heads” to
come up about 50 times if the coin is “fair.” In a study
of probability, it can be shown that the number of
heads h that appears in such an experiment should
satisfy the given inequality to be considered “fair.”
(a) Solve this inequality for h. (b) If you flipped a
coin 100 times and obtained 40 heads, is the coin
“fair”?
APPLICATIONS
Solve each application of absolute value.
61. Altitude of jet stream: To take advantage of the jet
stream, an airplane must fly at a height h (in feet)
that satisfies the inequality 冟h 35,050冟 2550.
Solve the inequality and determine if an altitude of
34,000 ft will place the plane in the jet stream.
62. Quality control tests: In order to satisfy quality
control, the marble columns a company produces
must earn a stress test score S that satisfies the
inequality 冟S 17,750冟 275. Solve the inequality
and determine if a score of 17,500 is in the passing
range.
63. Submarine depth: The sonar operator on a
submarine detects an old World War II submarine
net and must decide to detour over or under the
net. The computer gives him a depth model
冟d 394冟 20 7 164, where d is the depth in feet
that represents safe passage. At what depth should the
submarine travel to go under or over the net? Answer
using simple inequalities.
64. Optimal fishing depth: When deep-sea fishing,
the optimal depths d (in feet) for catching a
certain type of fish satisfy the inequality
28冟d 350冟 1400 6 0. Find the range of depths
that offer the best fishing. Answer using simple
inequalities.
For Exercises 65 through 68, (a) develop a model that
uses an absolute value inequality, and (b) solve.
65. Stock value: My stock in MMM Corporation
fluctuated a great deal in 2009, but never by more
than $3.35 from its current value. If the stock is
worth $37.58 today, what was its range in 2009?
66. Traffic studies: On a
given day, the volume
of traffic at a busy
intersection averages
726 cars per hour
(cph). During rush hour
the volume is much
higher, during “off
hours” much lower.
Find the range of this
volume if it never
varies by more than
235 cph from the
average.
67. Physical training for recruits: For all recruits in the
3rd Armored Battalion, the average number of sit-ups
is 125. For an individual recruit, the amount varies
by no more than 23 sit-ups from the battalion
average. Find the range of sit-ups for this battalion.
68. Computer consultant salaries: The national
average salary for a computer consultant is
$53,336. For a large computer firm, the salaries
offered to their employees vary by no more than
$11,994 from this national average. Find the range
of salaries offered by this company.
69. Tolerances for sport balls: According to the official
rules for golf, baseball, pool, and bowling, (a) golf
balls must be within 0.03 mm of d 42.7 mm,
(b) baseballs must be within 1.01 mm of
d 73.78 mm, (c) billiard balls must be within
0.127 mm of d 57.150 mm, and (d) bowling balls
must be within 12.05 mm of d 2171.05 mm. Write
each statement using an absolute value inequality,
then (e) determine which sport gives the least
width of interval
b for the diameter
tolerance t at average value
of the ball.
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70. Automated packaging: The machines that fill
boxes of breakfast cereal are programmed to fill
each box within a certain tolerance. If the box is
overfilled, the company loses money. If it is
underfilled, it is considered unsuitable for sale.
䊳
Suppose that boxes marked “14 ounces” of cereal
must be filled to within 0.1 oz. Find the acceptable
range of weights for this cereal.
EXTENDING THE CONCEPT
71. Determine the value or values (if any) that will
make the equation or inequality true.
x
a. 冟x冟 x 8
b. 冟x 2冟 2
c. x 冟x冟 x 冟x冟
d. 冟x 3冟 6x
e. 冟2x 1冟 x 3
72. The equation 冟5 2x冟 冟3 2x冟 has only one
solution. Find it and explain why there is only one.
73. In many cases, it can be helpful to view the solutions
to absolute value equations and inequalities as
follows. For any algebraic expression X and positive
䊳
2–42
CHAPTER 2 More on Functions
constant k, the equation 冟X冟 k has solutions X k
and X k, since the absolute value of either
quantity on the left will indeed yield the positive
constant k. Likewise, 冟X冟 6 k has solutions X 6 k
and X 6 k. Note the inequality symbol has not
been reversed as yet, but will naturally be reversed
as part of the solution process. Solve the following
equations or inequalities using this idea.
a. 冟x 3冟 5
b. 冟x 7冟 7 4
c. 3冟x 2冟 12
d. 3冟x 4冟 7 11
MAINTAINING YOUR SKILLS
74. (Appendix A.4) Factor the expression completely:
18x3 21x2 60x.
76. (Appendix A.6) Simplify
1
by rationalizing the
3 23
denominator. State the result in exact form and
approximate form (to hundredths).
75. (1.5) Solve V2 2W
for ␳ (physics).
C␳A
77. (Appendix A.3) Solve the inequality, then write the
solution set in interval notation:
312x 52 7 21x 12 7.
MID-CHAPTER CHECK
1. Determine whether the following function is even,
冟x冟
odd, or neither. f 1x2 x2 4x
2. Use a graphing calculator to find the maximum and
minimum values of
f 1x2 1.91x4 2.3x3 2.2x 5.12 . Round to
the nearest hundredth.
3. Use interval notation to identify the interval(s)
where the function from Exercise 2 is increasing,
decreasing, or constant. Round to the nearest
hundredth.
4. Write the equation of the function that has the same
graph of f 1x2 2x, shifted left 4 units and up 2
units.
5. For the graph given, (a) identify
the function family, (b) describe
or identify the end-behavior,
inflection point, and x- and
y-intercepts, (c) determine
the domain and range, and
(d) determine the value of k if
f 1k2 2.5. Assume required
features have integer values.
Exercise 5
y
5
f(x)
⫺5
5 x
⫺5
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Reinforcing Basic Concepts
6. Use a graphing calculator to graph the given
functions in the same window and comment on
what you observe.
p1x2 1x 32 2
r1x2 12 1x 32 2
147
9. Solve the following absolute value inequalities.
Write solutions in interval notation.
a. 3.1冟d 2冟 1.1 7.3
冟1 y冟
11
2 7
b.
3
2
c. 5冟k 2冟 3 6 4
q1x2 1x 32 2
7. Solve the following absolute value equations. Write
the solution in set notation.
2
11
a. 冟d 5冟 1 7
b. 5 冟s 3冟 3
2
10. Kiteboarding: With the correct sized kite, a person
can kiteboard when the wind is blowing at a speed
w (in mph) that satisfies the inequality 冟w 17冟 9.
Solve the inequality and determine if a person can
kiteboard with a windspeed of (a) 5 mph?
(b) 12 mph?
8. Solve the following absolute value inequalities.
Write solutions in interval notation.
x
a. 3冟q 4冟 2 6 10 b. ` 2 ` 5 5
3
REINFORCING BASIC CONCEPTS
Using Distance to Understand Absolute V alue Equations and Inequalities
For any two numbers a and b on the number line, the distance between a and b can be written 冟a b冟 or 冟b a冟. In exactly
the same way, the equation 冟x 3冟 4 can be read, “the distance between 3 and an unknown number is equal to 4.”
The advantage of reading it in this way (instead of “the absolute value of x minus 3 is 4”), is that a much clearer
visualization is formed, giving a constant reminder there are two solutions. In diagram form we have Figure 2.51.
Distance between
3 and x is 4.
⫺5 ⫺4 ⫺3 ⫺2
Figure 2.51
4 units
⫺1
0
1
4 units
2
3
4
5
Distance between
3 and x is 4.
6
7
8
9
From this we note the solutions are x 1 and x 7.
In the case of an inequality such as 冟x 2冟 3, we rewrite the inequality as 冟x 122 冟 3 and read it, “the distance
between 2 and an unknown number is less than or equal to 3.” With some practice, visualizing this relationship
mentally enables a quick statement of the solution: x 僆 35, 14 . In diagram form we have Figure 2.52.
Distance between 2
and x is less than or equal to 3.
8 7 6
Figure 2.52
3 units
Distance between 2
and x is less than or equal to 3.
3 units
5 4 3 2 1
0
1
2
3
4
5
6
Equations and inequalities where the coefficient of x is not 1 still lend themselves to this form of conceptual understanding. For 冟2x 1冟 3 we read, “the distance between 1 and twice an unknown number is greater than or equal to 3.”
On the number line (Figure 2.53), the number 3 units to the right of 1 is 4, and the number 3 units to the left of 1 is 2.
Distance between 1 and
2x is greater than or equal to 3.
Figure 2.53
3 units
6 5 4 3
ⴚ2 1
0
3 units
1
2
3
Distance between 1 and
2x is greater than or equal to 3
4
5
6
7
8
For 2x 2, x 1, and for 2x 4, x 2, and the solution set is x 僆 1q, 14 ´ 32, q 2.
Attempt to solve the following equations and inequalities by visualizing a number line. Check all results algebraically.
Exercise 1: 冟x 2冟 5
Exercise 2: 冟x 1冟 4
Exercise 3: 冟2x 3冟 5
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Precalculus—
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Basic Rational Functions and Power Functions;
More on the Domain
LEARNING OBJECTIVES
In Section 2.4 you will see
how we can:
A. Graph basic rational
functions, identify vertical
and horizontal
asymptotes, and describe
end-behavior
B. Use transformations to
graph basic rational
functions and write the
equation for a given
graph
C. Graph basic power
functions and state their
domains
D. Solve applications
involving basic rational
and power functions
In this section, we introduce two new kinds of relations, rational functions and power
functions. While we’ve already studied a variety of functions, we still lack the ability
to model a large number of important situations. For example, functions that model the
amount of medication remaining in the bloodstream over time, the relationship
between altitude and weightlessness, and the equations modeling planetary motion
come from these two families.
A. Rational Functions and Asymptotes
Just as a rational number is the ratio of two integers, a rational function is the ratio of
two polynomials. In general,
Rational Functions
A rational function V(x) is one of the form
V1x2 p1x2
d1x2
,
where p and d are polynomials and d1x2 0.
The domain of V(x) is all real numbers, except the zeroes of d.
The simplest rational functions are the reciprocal function y 1x and the reciprocal square function y x12, as both have a constant numerator and a single term in
the denominator. Since division by zero is undefined, the domain of both excludes
x 0. A preliminary study of these two functions will provide a strong foundation for
our study of general rational functions in Chapter 4.
The Reciprocal Function: y ⴝ
1
x
The reciprocal function takes any input (other than zero) and gives its reciprocal as the
output. This means large inputs produce small outputs and vice versa. A table of
values (Table 2.1) and the resulting graph (Figure 2.54) are shown.
Table 2.1
148
Figure 2.54
x
y
x
y
1000
1/1000
1/1000
1000
5
1/5
1/3
3
4
1/4
1/2
2
3
1/3
1
1
2
1/2
2
1/2
1
1
3
1/3
1/2
2
4
1/4
1/3
3
5
1/5
1/1000
1000
1000
1/1000
0
undefined
y
3
冢a, 3冣
y
1
x
2
(1, 1)
冢3, a冣
1
5
冢3, a冣
5
冢5, Q冣
(1, 1)
冢 a, 3冣
冢5, Q冣
x
1
2
3
2–44
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149
Section 2.4 Basic Rational Functions and Power Functions; More on the Domain
WORTHY OF NOTE
The notation used for graphical
behavior always begins by
describing what is happening to the
x-values, and the resulting effect on
the y-values. Using Figure 2.55,
visualize that for a point (x, y) on
the graph of y 1x , as x gets larger,
y must become smaller, particularly
since their product must always be
1 1y 1x 1 xy 12 .
Table 2.1 and Figure 2.54 reveal some interesting features. First, the graph passes
the vertical line test, verifying y 1x is indeed a function. Second, since division by
zero is undefined, there can be no corresponding point on the graph, creating a break
at x 0. In line with our definition of rational functions, the domain is
x 僆 1q, 02 ´ 10, q 2 . Third, this is an odd function, with a “branch” of the graph in
the first quadrant and one in the third quadrant, as the reciprocal of any input maintains
its sign. Finally, we note in QI that as x becomes an infinitely large positive number, y
becomes infinitely small and closer to zero. It seems convenient to symbolize this endbehavior using the following notation:
Figure 2.55
as x S q,
y
yS0
as x becomes an infinitely
large positive number
Graphically, the curve becomes very close to, or approaches the x-axis.
We also note that as x approaches zero from the right, y becomes an infinitely large
positive number: as x S 0 , y S q . Note a superscript or sign is used to indicate the direction of the approach, meaning from the positive side (right) or from the
negative side (left).
y
x
x
EXAMPLE 1
y approaches 0
䊳
Describing the End-Behavior of Rational Functions
For y 1x in QIII (Figure 2.54),
a. Describe the end-behavior of the graph.
b. Describe what happens as x approaches zero.
Solution
䊳
Similar to the graph’s behavior in QI, we have
a. In words: As x becomes an infinitely large negative number, y approaches zero.
In notation: As x S q , y S 0.
b. In words: As x approaches zero from the left, y becomes an infinitely large
negative number. In notation: As x S 0 , y S q .
Now try Exercises 7 and 8
The Reciprocal Square Function: y ⴝ
䊳
1
x2
From our previous work, we anticipate this graph will also have a break at x 0. But
since the square of any negative number is positive, the branches of the reciprocal
square function are both above the x-axis. Note the result is the graph of an even function. See Table 2.2 and Figure 2.56.
Table 2.2
Figure 2.56
x
y
x
y
1000
1/1,000,000
1/1000
1,000,000
5
1/25
1/3
9
4
1/16
1/2
4
3
1/9
1
1
2
1/4
2
1/4
1
1
3
1/9
1/2
4
4
1/16
1/3
9
5
1/25
1/1000
1,000,000
1000
1/1,000,000
0
undefined
y x12
y
3
(1, 1)
冢5,
1
1
25 冣
5
2
冢3, 19冣
(1, 1)
冢3, 19 冣
冢5,
5
1
2
3
1
25 冣
x
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CHAPTER 2 More on Functions
Similar to y 1x , large positive inputs generate small, positive outputs: as
x S q, y S 0. This is one indication of asymptotic behavior in the horizontal direction, and we say the line y 0 (the x-axis) is a horizontal asymptote for the reciprocal and reciprocal square functions. In general,
Horizontal Asymptotes
Given a constant k, the line y k is a horizontal asymptote for V if,
as x increases or decreases without bound, V(x) approaches k:
as x S q, V1x2 S k
or
as x S q, V1x2 S k
As shown in Figures 2.57 and 2.58, asymptotes are represented graphically as
dashed lines that seem to “guide” the branches of the graph. Figure 2.57 shows a horizontal asymptote at y 1, which suggests the graph of f(x) is the graph of y 1x
shifted up 1 unit. Figure 2.58 shows a horizontal asymptote at y 2, which suggests
the graph of g(x) is the graph of y x12 shifted down 2 units.
Figure 2.57
y
3
f(x) 1
x
Figure 2.58
1
y
3
2
2
y1
1
5
EXAMPLE 2
䊳
g(x) x12 2
5
x
1
5
5
1
1
2
2
3
3
x
y 2
Describing the End-Behavior of Rational Functions
For the graph in Figure 2.58, use mathematical notation to
a. Describe the end-behavior of the graph and name the horizontal asymptote.
b. Describe what happens as x approaches zero.
Solution
䊳
a. as x S q, g1x2 S 2,
as x S q, g1x2 S 2,
b. as x S 0 , g1x2 S q ,
as x S 0 , g1x2 S q
y 2 is a horizontal asymptote
Now try Exercises 9 and 10
䊳
While the graphical view of Example 2(a) (Figure 2.58) makes these concepts
believable, a numerical view of this end-behavior can be even more compelling. Try
entering x12 2 as Y1 on the Y= screen, then go to the TABLE feature 1TblStart 3,
¢Tbl 1; Figure 2.59). Scrolling in either direction shows that as 冟x冟 becomes very
large, Y1 becomes closer and closer to 2, but will never be equal to 2 (Figure 2.60).
Figure 2.59
Figure 2.60
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Section 2.4 Basic Rational Functions and Power Functions; More on the Domain
151
From Example 2(b), we note that as x becomes smaller and close to 0, g becomes
very large and increases without bound. This is one indication of asymptotic behavior
in the vertical direction, and we say the line x 0 (the y-axis) is a vertical asymptote
for g (x 0 is also a vertical asymptote for f in Figure 2.57). In general,
Vertical Asymptotes
Given a constant h, the vertical line x h is a vertical asymptote for a function V if,
as x approaches h, V(x) increases or decreases without bound:
as x S h , V1x2 S q
or
as x S h , V1x2 S q
Here is a brief summary:
Reciprocal Function
f 1x2 A. You’ve just seen how
we can graph basic rational
functions, identify vertical and
horizontal asymptotes, and
describe end-behavior
1
x
Domain: x 僆 1q, 02 ´ 10, q 2
Range: y 僆 1q, 02 ´ 10, q2
Horizontal asymptote: y 0
Vertical asymptote: x 0
Reciprocal Quadratic Function
1
x2
Domain: x 僆 1q, 02 ´ 10, q2
Range: y 僆 10, q 2
Horizontal asymptote: y 0
Vertical asymptote: x 0
g1x2 B. Using Asymptotes to Graph Basic Rational Functions
Identifying these asymptotes is useful because the graphs of y 1x and y x12 can be
transformed in exactly the same way as the toolbox functions. When their graphs
shift — the vertical and horizontal asymptotes shift with them and can be used as
guides to redraw the graph. In shifted form,
a
k for the reciprocal function, and
f 1x2 xh
a
k for the reciprocal square function.
g1x2 1x h2 2
When horizontal and/or vertical shifts are applied to simple rational functions, we
first apply them to the asymptotes, then calculate the x- and y-intercepts as before. An
additional point or two can be computed as needed to round out the graph.
EXAMPLE 3
䊳
Graphing Transformations of the Reciprocal Function
1
1 using transformations of the parent function.
x2
1
The graph of g is the same as that of y , but shifted 2 units right and 1 unit upward.
x
This means the vertical asymptote is also shifted 2 units right, and the horizontal
1
asymptote is shifted 1 unit up. The y-intercept is g102 . For the x-intercept:
2
1
1 substitute 0 for g (x )
0
x2
1
1 subtract 1
x2
11x 22 1
multiply by 1x 22
x1
solve
Sketch the graph of g1x2 Solution
y
5
䊳
x2
4
3
y1
5
(0, 0.5)
(1, 0)
2
1
1
2
3
4
5
5
x
The x-intercept is (1, 0). Knowing the graph is from the reciprocal function family
and shifting the asymptotes and intercepts yields the graph shown.
Now try Exercises 11 through 26
䊳
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CHAPTER 2 More on Functions
These ideas can be “used in reverse” to determine the equation of a basic rational
function from its given graph, as in Example 4.
EXAMPLE 4
䊳
Writing the Equation of a Basic Rational Function, Given Its Graph
Identify the function family for the graph given, then use
the graph to write the equation of the function in “shifted
form.” Assume 冟a冟 1.
Solution
䊳
The graph appears to be from the reciprocal square
family, and has been shifted 2 units right (the vertical
asymptote is at x 2), and 1 unit down (the horizontal
asymptote is at y 1). From y x12 , we obtain
f 1x2 1x 1 22 2 1 as the shifted form.
y
6
6
6 x
6
Now try Exercises 27 through 38
B. You’ve just seen how
we can use asymptotes and
transformations to graph basic
rational functions and write the
equation for a given graph
䊳
Using the definition of negative exponents, the basic reciprocal and reciprocal
square functions can be written as y x1 and y x2, respectively. In this form, we
note that these functions also belong to a family of functions known as the power functions (see Exercise 80).
C. Graphs of Basic Power Functions
Italian physicist and astronomer Galileo Galilei (1564–1642) made numerous contributions to astronomy, physics, and other fields. But perhaps he is best known for his
experiments with gravity, in which he dropped objects of different weights from the
Leaning Tower of Pisa. Due in large part to his work, we know that the velocity of an
object after it has fallen a certain distance is v 12gs, where g is the acceleration due
to gravity (32 ft/sec2), s is the distance in feet the object has fallen, and v is the velocity of the object in feet per second (see Exercise 71). As you will see, this is an example of a formula that uses a power function.
From previous coursework or a review of radicals
and rational
exponents (Ap1
1
3
pendix A.6), we know that 1x can be written1 as x2, and 1 x1 as x3, enabling us to write
these functions in exponential form: f 1x2 x2 and g1x2 x3. In this form, we see that
these actually belong to a larger family of functions, where x is raised to some power,
called the power functions.
Power Functions and Root Functions
For any constant real number p and variable x, functions of the form
f 1x2 x p
are called power functions in x. If p is of the form
1
for integers n 2, the functions
n
f 1x2 xn 3 f 1x2 1 x
1
are called root functions in x.
n
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Section 2.4 Basic Rational Functions and Power Functions; More on the Domain
1
3
5
y x2, y x4, y x3, y 1
x, and y x2 are all power functions,
The functions
1
5
4
but only y x and y 1 x are also root functions. Initially we will focus on
power functions where p 7 0.
EXAMPLE 5
䊳
Comparing the Graphs of P ower Functions
Use a graphing calculator
to graph the power functions f 1x2 x4 , g1x2 x3 ,
3
1
2
h1x2 x , p1x2 x , and q1x2 x2 in the standard viewing window. Make an
observation in QI regarding the effect
of the 7exponent on each function, then
1
discuss what the graphs of y x6 and y x2 would look like.
1
Solution
䊳
First we enter the functions in sequence
as Y1 through Y5 on the Y= screen
(Figure 2.61). Using ZOOM 6:ZStandard
produces the graphs shown in
Figure 2.62. Narrowing the window
to focus on QI (Figure 2.63:
x 僆 3 4, 104, y 僆 34, 10 4 ), we
quickly see that for x 1, larger
values of p cause the graph of y x p
to increase at a faster rate, and smaller
values at a slower rate. In other words
1
1
(for x 1), since 6 , the graph of
6
4
1
y x6 would increase slower and appear
1
to be “under” the graph of Y1 X4 .
7
7
Since 7 2, the graph of y x2 would
2
increase faster and appear to be “more
narrow” than the graph of Y5 X2
(verify this).
2
Figure 2.61, 2.62
10
10
10
10
Figure 2.63
10 Y5
Y4
Y3
Y2
Y1
4
10
4
Now try Exercises 39 through 48
䊳
The Domain of a Power Function
In addition to the observations made in Example 5, we can make other important notes,
particularly regarding the domains of power functions. When the exponent on a power
m
function is a rational number
7 0 in simplest form, it appears the domain is all real
n
2
1
numbers if n 2 is odd, as seen in the graphs of g1x2 x3 , h1x2 x1 x1 , and
2
q1x2 x x1. If n is an even1 number, the domain
is all nonnegative real numbers as
3
seen in the graphs of f 1x2 x4 and p1x2 x2. Further exploration will show that if p is
irrational, as in y x␲, the domain is also all nonnegative real numbers and we have
the following:
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The Domain of a P ower Function
Given a power function f 1x2 x p with p 7 0.
m
1. If p is a rational number in simplest form,
n
a. the domain of f is all real numbers if n is odd: x 僆 1q, q 2 ,
b. the domain of f is all nonnegative real numbers if n is even: x 僆 3 0, q 2 .
2. If p is an irrational number, the domain of f is all nonnegative real numbers:
x 僆 30, q 2 .
Further confirmation
of statement
1 can be found by recalling the graphs of
1
1
3
y 1x x2 and y 1
x x3 from Section 2.2 (Figures 2.64 and 2.65).
Figure 2.64
y
Figure 2.65
f(x) ⫽ 兹x
5
5
(note n is even)
(9, 3)
(4, 2) (6, 2.4)
(0, 0)
⫺1
(note n is odd)
(8, 2)
(1, 1)
(0, 0)
4
8
3
y g(x) ⫽ 兹x
x
⫺8
⫺4
(1, 1)
4
8
x
(⫺1, ⫺1)
(⫺8, ⫺2)
⫺5
⫺5
Domain: x 僆 30, q2
Range: y 僆 3 0, q 2
EXAMPLE 6
Solution
䊳
Domain: x 僆 3q, q2
Range: y 僆 3q, q2
Determining the Domains of P ower Functions
State the domain of the following power functions, and identity whether each is
also a root function.
4
1
2
8
a. f 1x2 x5 b. g1x2 x10 c. h1x2 1 x d. q1x2 x3 e. r 1x2 x1 5
䊳
a. Since n is odd, the domain of f is all real numbers; f is not a root function.
b. Since n is even, the domain of g is x 僆 冤0, q 2 ; g is a root function.
1
c. In exponential form h1x2 x8 . Since n is even, the domain of h is x 僆 冤0, q 2 ;
h is a root function.
d. Since n is odd, the domain of q is all real numbers; q is not a root function
e. Since p is irrational, the domain of r is x 僆 冤0, q 2 ; r is not a root function
Now try Exercises 49 through 58
䊳
Transformations of Power and Root Functions
As we saw in Section 2.2 (Toolbox Functions and Transformations), the graphs of the
3
root functions y 1x and y 1 x can be transformed using shifts, stretches,
reflections, and so on. In Example 8(b) (Section 2.2) we noted the graph of
3
3
h1x2 2 1
x 2 1 was the graph of y 1
x shifted 2 units right, stretched by a
factor of 2, and shifted 1 unit down. Graphs of other power functions can be transformed in exactly the same way.
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Section 2.4 Basic Rational Functions and Power Functions; More on the Domain
EXAMPLE 7
䊳
Graphing Transformations of Power Functions
Based on our previous observations,
2
3
a. Determine the domain of f 1x2 x3 and g1x2 x2 , then verify by graphing
them on a graphing calculator.
2
3
b. Next, discuss what the graphs of F1x2 1x 22 3 3 and G1x2 x2 2
will look like, then graph each on a graphing calculator to verify.
Solution
䊳
m
a. Both f and g are power functions of the form y x n . For f, n is odd so its
domain is all real numbers. For g, n is even and the domain is x 僆 30, q2 .
Their graphs support this conclusion (Figures 2.66 and 2.67).
Figure 2.66
Figure 2.67
10
10
10
10
10
10
10
10
b. The graph of F will be the same as the graph of f, but shifted two units right
and three units down, moving the vertex to 12, 32 . The graph of G will be the
same as the graph of g, but reflected across the x-axis, and shifted 2 units up
(Figures 2.68 and 2.69).
Figure 2.69
Figure 2.68
10
10
C. You’ve just seen how
we can graph basic power
functions and state their
domains
10
10
10
10
10
10
Now try Exercises 59 through 62
䊳
D. Applications of Rational and Power Functions
These new functions have a variety of interesting and significant applications in the
real world. Examples 8 through 10 provide a small sample, and there are a number of
additional applications in the Exercise Set. In many applications, the coefficients may
be rather large, and the axes should be scaled accordingly.
EXAMPLE 8
䊳
Modeling the Cost to Remo ve Waste
For a large urban-centered county, the cost to remove chemical waste and other
18,000
180,
pollutants from a local river is given by the function C1p2 p 100
where C( p) represents the cost (in thousands of dollars) to remove p percent of
the pollutants.
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CHAPTER 2 More on Functions
a. Find the cost to remove 25%, 50%, and 75% of the pollutants and comment on
the results.
b. Graph the function using an appropriate scale.
c. Use mathematical notation to state what happens as the county attempts to
remove 100% of the pollutants.
Solution
䊳
a. We evaluate the function as indicated, finding that C1252 60, C1502 180,
and C1752 540. The cost is escalating rapidly. The change from 25% to 50%
brought a $120,000 increase, but the change from 50% to 75% brought a
$360,000 increase!
C(p)
b. From the context, we need only graph the
x ⫽ 100
1200
portion from 0 p 6 100. For the C-intercept
we substitute p 0 and find C102 0, which
900
seems reasonable as 0% would be removed
(75, 540)
600
if $0 were spent. We also note there must be
a vertical asymptote at x 100, since this
300
x-value causes a denominator of 0. Using
(25, 60)
(50, 180)
p
this information and the points from part (a)
100
50
75
25
produces the graph shown.
c. As the percentage of pollutants removed
y ⫽ ⫺180
approaches 100%, the cost of the cleanup
skyrockets. Using notation: as p S 100 , C S q .
Now try Exercises 65 through 70
䊳
While not obvious at first, the function C(p) in Example 8 is from the family of
1
reciprocal functions y . A closer inspection shows it has the form
x
18,000
1
a
k S
180, showing the graph of y is shifted right
y
x
xh
x 100
100 units, reflected across the x-axis, stretched by a factor of 18,000 and shifted 180 units
down (the horizontal asymptote is y 180). As sometimes occurs in real-world
applications, portions of the graph were ignored due to the context. To see the full
graph, we reason that the second branch occurs on the opposite side of the vertical and
horizontal asymptotes, and set the window as shown in Figure 2.70. After entering
C(p) as Y1 on the Y= screen and pressing GRAPH , the full graph appears as shown in
Figure 2.71 (for effect, the vertical and horizontal asymptotes were drawn separately
using the 2nd PRGM (DRAW) options).
Figure 2.71
Figure 2.70
2000
200
0
2000
Next, we’ll use a root function to model the distance to the horizon from a
given height.
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Section 2.4 Basic Rational Functions and Power Functions; More on the Domain
EXAMPLE 9
䊳
The Distance to the Horizon
On a clear day, the distance a person can see from a certain height (the distance to
the horizon) is closely approximated by the root function d1h2 3.571h, where
d(h) represents the viewing distance (in kilometers) from a height of h meters
above sea level.
a. To the nearest kilometer, how far can a person see when standing on the
observation level of the John Hancock building in Chicago, Illinois, about 335 m
high?
b. To the nearest meter, how high is the observer’s eyes, if the viewing distance is
130 km?
Solution
䊳
a. Substituting 335 for h we have
d1h2 3.57 1h
d13352 3.57 1335
⬇ 65.34
original function
substitute 335 for h
result
On a clear day, a person can see about 65 kilometers.
b. We substitute 130 for d(h):
d1h2
130
36.415
1326.052
3.57 1h
3.57 1h
⬇ 1h
⬇h
original function
substitute 130 for d(h)
divide by 3.57
square both sides
If the distance to the horizon is 130 km, the observer’s eyes are at a
height of approximately 1326 m. Check the answer to part (b) by solving
graphically.
Now try Exercises 71 through 74
䊳
One area where power functions and modeling with regression are used extensively is allometric studies. This area of inquiry studies the relative growth of a
part of an animal in relation to the growth of the whole, like the wingspan of a bird
compared to its weight, or the daily food intake of a mammal or bird compared to
its size.
EXAMPLE 10
䊳
Modeling the Food Requirements of Cer tain Bird Species
To study the relationship between the
weight of a nonpasserine bird and its
daily food intake, the data shown in the
table was collected (nonpasserine:
nonsinging, nonperching birds).
a. On a graphing calculator, enter the
data in L1 and L2, then set an
appropriate window to view a
scatterplot of the data. Does a power
regression STAT CALC, A:PwrReg
seem appropriate?
Average
weight (g)
Daily food
intake (g)
Common
pigeon
350
25
Ring-necked
duck
725
50
Ring-necked
pheasant
1400
70
Canadian
goose
4525
165
White
swan
9075
240
Bird
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b. Use a graphing calculator to find an equation model using a power regression
on the data, and enter the equation in Y1 (round values to three decimal
places).
c. Use the equation to estimate the daily food intake required by a barn owl (470 g),
and a gray-headed albatross (6800 g).
d. Use the intersection of graphs method to find the weight of a Great-Spotted
Kiwi, given the daily food requirement is 130 g.
Solution
䊳
a. After entering the weights in L1 and
Figure 2.72
food intake in L2, we set a window that
300
will comfortably fit the data. Using
x 僆 30, 10,000 4 and y 僆 330, 300 4
produces the scatterplot shown
(Figure 2.72). The data does not appear 0
10,000
linear, and based on our work in
Example 5, a power function seems
appropriate.
30
b. To access the power regression option,
use STAT
(CALC) A:PwrReg. To
Figure 2.73
three decimal places the equation for Y1
would be 0.493 X0.685 (Figure 2.73).
c. For the barn owl, x 470 and we find the
estimated food requirement is about
33.4 g per day (Figure 2.74). For the grayheaded albatross x 6800 and the model
estimates about 208.0 g of food daily is
required.
d. Here we’re given the food intake of the Great-Spotted Kiwi (the output value),
and want to know what input value (weight) was used. Entering Y2 130,
we’ll attempt to find where the graphs of Y1 and Y2 intersect (it will help to
deactivate Plot1 on the Y= screen, so that only the graphs of Y1 and Y2
appear). Using 2nd TRACE (CALC) 5:Intersect shows the graphs intersect at
about (3423.3, 130) (Figure 2.75), indicating the average weight of a
Great-Spotted Kiwi is near 3423.3 g (about 7.5 lb).
Figure 2.75
Figure 2.74
300
10,000
0
D. You’ve just seen how
we can solve applications
involving basic rational and
power functions
30
Now try Exercises 75 through 78
䊳
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159
2.4 EXERCISES
䊳
CONCEPTS AND VOCABULAR Y
Fill in each blank with the appropriate word or phrase. Carefully reread the section if needed.
1. Write the following in notational form. As x
becomes an infinitely large negative number, y
approaches 2.
1
2,
1x 32 2
a
asymptote occurs at x 3 and
a horizontal asymptote at
.
䊳
2. For any constant k, the notation “as 冟 x 冟 S q, y S k ”
is an indication of a
asymptote, while
“x S k, 冟y冟 S q ” indicates a
asymptote.
1
has branches in Quadrants I
x
1
and III. The graph of Y2 has branches in
x
Quadrants
and
.
3. Given the function g1x2 4. The graph of Y1 5. Discuss/Explain how and why the range of the
reciprocal function differs from the range of the
reciprocal quadratic function. In the reciprocal
quadratic function, all range values are positive.
6. If the graphs of Y1 1
1
and Y2 2 were drawn
x
x
on the same grid, where would they intersect? In
what interval(s) is Y1 7 Y2?
DEVELOPING YOUR SKILLS
For each graph given, (a) use mathematical notation
to describe the end-behavior of each graph and
(b) describe what happens as x approaches 1.
1
2
x1
7. V1x2 8. v1x2 1
2
x1
y
y
6
5
4
3
2
1
⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
3
2
1
1 2 3 4 5 6 x
1
x
⫺5⫺4⫺3⫺2⫺1
⫺1 1 2 3 4 5
⫺2
⫺3
⫺4
⫺5
⫺6
⫺7
For each graph given, (a) use mathematical notation to
describe the end-behavior of each graph, (b) name the
horizontal asymptote, and (c) describe what happens as
x approaches ⴚ2.
9. Q1x2 1
1
1 10. q1x2 2
2
1x 22
1x 22 2
y
⫺7⫺6⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
y
5
4
3
2
1
6
5
4
3
2
1
1 2 3 x
⫺7⫺6⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
⫺5
Sketch the graph of each function using transformations
of the parent function (not by plotting points). Clearly
state the transformations used, and label the horizontal
and vertical asymptotes as well as the x- and
y-intercepts (if they exist). Also state the domain
and range of each function.
11. f 1x2 12. g1x2 13.
14.
15.
17.
19.
21.
23.
25.
1 2 3 x
1
1
x
1
h1x2 x2
1
g1x2 x2
1
f 1x2 1
x2
1
h1x2 1x 12 2
1
g1x2 1x 22 2
1
f 1x2 2 2
x
1
h1x2 1 1x 22 2
16.
18.
20.
22.
24.
26.
1
2
x
1
f 1x2 x3
1
h1x2 2
x
1
g1x2 2
x3
1
f 1x2 1x 52 2
1
h1x2 2 2
x
1
g1x2 2 3
x
1
g1x2 2 1x 12 2
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Identify the parent function for each graph given, then
use the graph to construct the equation of the function
in shifted form. Assume |a| ⴝ 1.
y
27.
S(x)
⫺6⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
⫺5
⫺6
y
28.
4
3
2
1
5
4
3
2
1
1 2 3 4 x
⫺7⫺6⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
s(x)
⫺3
⫺4
⫺5
1 2 3 x
For each pair of functions given, state which function
increases faster for x ⬎ 1, then use the INTERSECT
command of a graphing calculator to find where
(a) f(x) ⫽ g(x), (b) f(x) ⬎ g(x), and (c) f(x) ⬍ g(x).
39. f 1x2 x2, g1x2 x3
40. f 1x2 x4, g1x2 x5
43. f 1x2 x , g1x2 x
44. f 1x2 x 4, g1x2 x2
41. f 1x2 x4, g1x2 x2
2
3
42. f 1x2 x3, g1x2 x5
4
5
7
6
3
5
4
45. f 1x2 1
x, g1x2 1
x 46. f 1x2 1
x, g1x2 1
x
3 2
4 3
47. f 1x2 2
x , g1x2 x4 48. f 1x2 x2, g1x2 2
x
5
29.
3
2
1
y
4
3
2
1
Q(x)
⫺6⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
⫺5
⫺6
⫺7
31.
30.
y
1 2 3 4 x
⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
⫺5
⫺6
y
2
1
⫺7⫺6⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
v(x)
⫺3
⫺4
⫺5
⫺6
⫺7
⫺8
1 2 3 x
q(x)
y
2
1
⫺7⫺6⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
w(x)
⫺3
⫺4
⫺5
⫺6
⫺7
⫺8
1 2 3 x
Use the graph shown to
Exercises 33 through 38
y
complete each statement using
10
the direction/approach notation.
33. As x S q, y ______.
34. As x S q, y ______.
⫺10
10 x
35. As x S 1, y ______.
49. f 1x2 x8
7
50. g1x2 x7
51. h1x2 x5
6
52. q1x2 x6
7
53. r1x2 1
x
54. s1x2 x6
6
5
1
Using the functions from Exercises 49–54, identify
which of the following are defined and which are not.
Do not use a calculator or evaluate.
55. a. f 122
b. f(2)
56. a. h(0.3)
b. h10.32 c. q(0.3)
d. q(0.3)
57. a. h11.22
b. r172
d. s(0)
7
58. a. f a b
8
8
b. ga b c. q11.92
7
c. g122
36. As x S 1 , y ______.
⫺10
37. The line x 1 is a vertical asymptote, since: as
x S ____, y S ____.
38. The line y 2 is a horizontal asymptote, since:
as x S ____, y S ____.
c. s1␲2
d. g122
d. q(0)
Compare and discuss the graphs of the following
functions. Verify your answer by graphing both on a
graphing calculator.
59. f 1x2 x8; F1x2 1x 12 8 2
7
䊳
3
State the domain of the following functions.
1 2 3 4 5 6 x
32.
3
7
60. g1x2 x7; G1x2 1x 32 7 2
8
8
6
6
61. p1x2 x5; P1x2 1x 22 5
5
5
62. q1x2 x6; Q1x2 2x6 5
WORKING WITH FORMULAS
63. Gravitational attraction: F ⴝ
km1m2
2
d
The gravitational force F between two objects with
masses m1 and m2 depends on the distance d
between them and some constant k. (a) If the
masses of the two objects are constant while the
distance between them gets larger and larger, what
happens to F? (b) Let m1 and m2 equal 1 mass unit
with k 1 as well, and investigate using a table of
values. What family does this function belong to?
(c) Solve for m2 in terms of k, m1, d and F.
mⴙM
22gh
m
For centuries, the velocity v of a bullet of mass m
has been found using a device called a ballistic
pendulum. In one such device, a bullet is fired into
a stationary block of wood of mass M, suspended
from the end of a pendulum. The height h the
pendulum swings after impact is measured, and the
approximate velocity of the bullet can then be
calculated using g 9.8 m/sec2 (acceleration due
to gravity). When a .22-caliber bullet of mass 2.6 g
is fired into a wood block of mass 400 g, their
combined mass swings to a height of 0.23 m. To
the nearest meter per second, find the velocity of
the bullet the moment it struck the wood.
64. Velocity of a bullet: v ⴝ
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Section 2.4 Basic Rational Functions and Power Functions; More on the Domain
161
APPLICATIONS
65. Deer and predators: By banding deer over a
period of 10 yr, a capture-and-release project
determines the number of deer per square mile in
the Mark Twain National Forest can be modeled by
75
the function D1p2 , where p is the number of
p
predators present and D is the number of deer. Use
this model to answer the following.
a. As the number of predators increases, what
will happen to the population of deer? Evaluate
the function at D(1), D(3), and D(5) to verify.
b. What happens to the deer population if the
number of predators becomes very large?
c. Graph the function using an appropriate scale.
Judging from the graph, use mathematical
notation to describe what happens to the deer
population if the number of predators becomes
very small (less than 1 per square mile).
66. Balance of nature: A marine biology research
group finds that in a certain reef area, the number
of fish present depends on the number of sharks in
the area. The relationship can be modeled by the
20,000
, where F(s) is the fish
function F1s2 s
population when s sharks are present.
a. As the number of sharks increases, what will
happen to the population of fish? Evaluate the
function at F(10), F(50), and F(200) to verify.
b. What happens to the fish population if the
number of sharks becomes very large?
c. Graph the function using an appropriate scale.
Judging from the graph, use mathematical
notation to describe what happens to the fish
population if the number of sharks becomes
very small.
67. Intensity of light: The intensity I of a light source
depends on the distance of the observer from the
source. If the intensity is 100 W/m2 at a distance of
5 m, the relationship can be modeled by the
2500
function I1d2 2 . Use the model to answer the
d
following.
a. As the distance from the lightbulb increases,
what happens to the intensity of the light?
Evaluate the function at I(5), I(10), and I(15)
to verify.
b. If the intensity is increasing, is the observer
moving away or toward the light source?
c. Graph the function using an appropriate scale.
Judging from the graph, use mathematical
notation to describe what happens to the
intensity if the distance from the lightbulb
becomes very small.
68. Electrical resistance: The resistance R (in ohms)
to the flow of electricity is related to the length of
the wire and its gauge (diameter in fractions of an
inch). For a certain wire with fixed length, this
relationship can be modeled by the function
0.2
R1d2 2 , where R(d) represents the resistance in
d
a wire with diameter d.
a. As the diameter of the wire increases, what
happens to the resistance? Evaluate the
function at R(0.05), R(0.25), and R(0.5) to
verify.
b. If the resistance is increasing, is the diameter
of the wire getting larger or smaller?
c. Graph the function using an appropriate scale.
Judging from the graph, use mathematical
notation to describe what happens to the
resistance in the wire as the diameter gets
larger and larger.
69. Pollutant removal: For a certain coal-burning
power plant, the cost to remove pollutants from
plant emissions can be modeled by
8000
80, where C(p) represents the
C1p2 p 100
cost (in thousands of dollars) to remove p percent of
the pollutants. (a) Find the cost to remove 20%,
50%, and 80% of the pollutants, then comment on
the results; (b) graph the function using an
appropriate scale; and (c) use mathematical notation
to state what happens if the power company
attempts to remove 100% of the pollutants.
70. City-wide recycling: A large city has initiated a
new recycling effort, and wants to distribute
recycling bins for use in separating various
recyclable materials. City planners anticipate the
cost of the program can be modeled by the
22,000
220, where C(p)
function C1p2 p 100
represents the cost (in $10,000) to distribute the
bins to p percent of the population. (a) Find the
cost to distribute bins to 25%, 50%, and 75% of
the population, then comment on the results;
(b) graph the function using an appropriate scale;
and (c) use mathematical notation to state what
happens if the city attempts to give recycling bins
to 100% of the population.
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71. Hot air ballooning: If air resistance is neglected,
the velocity (in ft/s) of a falling object can be closely
approximated by the function V1s2 8 1s, where s
is the distance the object has fallen (in feet). A
balloonist suddenly finds it necessary to release
some ballast in order to quickly gain altitude.
(a) If she were flying at an altitude of 1000 ft, with
what velocity will the ballast strike the ground?
(b) If the ballast strikes the ground with a velocity of
225 ft/sec, what was the altitude of the balloon?
72. River velocities: The ability of a river or stream to
move sand, dirt, or other particles depends on the
size of the particle and the velocity of the river.
This relationship can be used to approximate the
velocity (in mph) of the river using the function
V1d2 1.77 1d, where d is the diameter (in
inches) of the particle being moved. (a) If a creek
can move a particle of diameter 0.095 in., how fast
is it moving? (b) What is the largest particle that
can be moved by a stream flowing 1.1 mph?
73. Shoe sizes: Although there may be some notable
exceptions, the size of shoe worn by the average
man is related to his height. This relationship
is
3
modeled by the function S1h2 0.75h2, where h is
the person’s height in feet and S is the U.S. shoe
size. (a) Approximate Denzel Washington’s shoe
size given he is 6 ft, 0 in. tall. (b) Approximate
Dustin Hoffman’s height given his shoe size is 9.5.
74. Whale weight: For a certain species of whale, the
relationship between the length of the whale and the
weight of the 27whale can be modeled by the function
W1l2 0.03l 11, where l is the length of the whale
in meters and W is the weight of the whale in metric
tons (1 metric ton ⬇ 2205 pounds). (a) Estimate the
weight of a newborn calf that is 6 m long. (b) At 81
metric tons, how long is an average adult?
75. Gestation periods: The data shown in the table
can be used to study the relationship between the
weight of mammal and its length of pregnancy. Use
a graphing calculator to (a) graph a scatterplot of
the data and (b) find an equation model using a
power regression (round to three decimal places).
Use the equation to estimate (c) the length of
pregnancy of a racoon (15.5 kg) and (d) the weight
of a fox, given the length of pregnancy is 52 days.
Average
Weight (kg)
Gestation
(days)
Rat
0.4
24
Rabbit
3.5
50
Armadillo
6.0
51
Coyote
13.1
62
Dog
24.0
64
Mammal
76. Bird wingspans: The data in the table explores the
relationship between a bird’s weight and its
wingspan. Use a graphing calculator to (a) graph a
scatterplot of the data and (b) find an equation
model using a power regression (round to three
decimal places). Use the equation to estimate (c) the
wingspan of a Bald Eagle (16 lb) and (d) the weight
of a Bobwhite Quail with a wingspan of 0.9 ft.
Weight Wingspan
(lb)
(ft)
Bird
Golden Eagle
10.5
6.5
Horned Owl
3.1
2.6
Peregrine Falcon
3.3
4.0
Whooping Crane
17.0
7.5
1.5
2.0
Raven
77. Species-area relationship: To study the relationship
between the number of species of birds on islands in
the Caribbean, the data shown in the table was
collected. Use a graphing calculator to (a) graph a
scatterplot of the data and (b) find an equation model
using a power regression (round to three decimal
places). Use the equation to estimate (c) the number
of species of birds on Andros (2300 mi2) and (d) the
area of Cuba, given there are 98 such species.
Island
Area (mi2)
Great Inagua
Species
600
16
Trinidad
2000
41
Puerto Rico
3400
47
4500
38
30,000
82
Jamaica
Hispaniola
78. Planetary orbits: The table shown gives the time
required for the first five planets to make one
complete revolution around the Sun (in years), along
with the average orbital radius of the planet in
astronomical units (1 AU 92.96 million miles).
Use a graphing calculator to (a) graph a scatterplot of
the data and (b) find an equation model using a
power regression (round to four decimal places). Use
the equation to estimate (c) the average orbital radius
of Saturn, given it orbits the Sun every 29.46 yr, and
(d) estimate how many years it takes Uranus to orbit
the Sun, given it has an average orbital radius of
19.2 AU.
Planet
Years
Radius
Mercury
0.24
0.39
Venus
0.62
0.72
Earth
1.00
1.00
1.88
1.52
11.86
5.20
Mars
Jupiter
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Section 2.5 Piecewise-Defined Functions
EXTENDING THE CONCEPT
79. Consider the graph of f 1x2 1
once again, and the
x
x by f(x) rectangles mentioned in the Worthy of
Note on page 149. Calculate the area of each
rectangle formed for x 僆 51, 2, 3, 4, 5, 66 . What do
1
you notice? Repeat the exercise for g1x2 2 and
x
the x by g(x) rectangles. Can you detect the pattern
formed here?
80. All of the power functions presented in this section
had positive exponents, but the definition of these
types of functions does allow for negative exponents
as well. In addition to the reciprocal and reciprocal
square functions (y x1 and y x2), these types
䊳
163
of power functions have
Depth
Temp
significant applications. For
(meters)
(°C)
example, the temperature of
125
13.0
ocean water depends on several
250
9.0
factors, including salinity,
500
6.0
latitude, depth, and density.
750
5.0
However, between depths of
125 m and 2000 m, ocean
1000
4.4
temperatures are relatively
1250
3.8
predictable, as indicated by the
1500
3.1
data shown for tropical oceans
1750
2.8
in the table. Use a graphing
2000
2.5
calculator to find the power
regression model and use it to estimate the water
temperature at a depth of 2850 m.
MAINTAINING YOUR SKILLS
81. (1.4) Solve the equation for y, then sketch its graph
using the slope/intercept method: 2x 3y 15.
82. (1.3) Using a scale from 1 (lousy) to 10 (great),
Charlie gave the following ratings: {(The Beatles,
9.5), (The Stones, 9.6), (The Who, 9.5), (Queen, 9.2),
(The Monkees, 6.1), (CCR, 9.5), (Aerosmith, 9.2),
(Lynyrd Skynyrd, 9.0), (The Eagles, 9.3), (Led
2.5
Zeppelin, 9.4), (The Stones, 9.8)}. Is the relation
(group, rating) as given, also a function? State why
or why not.
83. (1.5) Solve for c: E mc2.
84. (2.3) Use a graphing calculator to solve
冟x 2冟 1 2冟x 1冟 3.
Piecewise-Defined Functions
LEARNING OBJECTIVES
In Section 2.5 you will see
how we can:
A. State the equation,
domain, and range of
a piecewise-defined
function from its graph
B. Graph functions that are
piecewise-defined
C. Solve applications
involving piecewisedefined functions
Most of the functions we’ve studied thus far have been smooth and continuous.
Although “smooth” and “continuous” are defined more formally in advanced
courses, for our purposes smooth simply means the graph has no sharp turns or
jagged edges, and continuous means you can draw the entire graph without lifting
your pencil. In this section, we study a special class of functions, called piecewisedefined functions, whose graphs may be various combinations of smooth/not
smooth and continuous/not continuous. The absolute value function is one example (see Exercise 31). Such functions have a tremendous number of applications in
the real world.
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A. The Domain of a Piecewise-Defined Function
For the years 1990 to 2000, the American bald eagle remained on the nation’s endangered species list, although the number of breeding pairs was growing slowly. After
2000, the population of eagles grew
at a much faster rate, and they were
removed from the list soon afterward. From Table 2.3 and plotted
points modeling this growth (see
Figure 2.76), we observe that a linear
model would fit the period from
1992 to 2000 very well, but a line
with greater slope would be needed
for the years 2000 to 2006 and (perhaps) beyond.
Figure 2.76
10,000
Bald eagle breeding pairs
9,000
Table 2.3
Year
(1990 S 0)
Bald Eagle
Breeding Pairs
Year
(1990 S 0)
Bald Eagle
Breeding Pairs
2
3700
10
6500
4
4400
12
7600
6
5100
14
8700
8
5700
16
9800
8,000
7,000
6,000
5,000
4,000
3,000
Source: www.fws.gov/midwest/eagle/population
0
2
4
6
8
10
12
14
16
18
t (years since 1990)
WORTHY OF NOTE
For the years 1992 to 2000, we can
estimate the growth in breeding
pairs ¢pairs
¢time using the points (2, 3700)
and (10, 6500) in the slope formula.
The result is 350
1 , or 350 pairs per
year. For 2000 to 2006, using (10,
6500) and (16, 9800) shows the rate
of growth is significantly larger:
¢pairs
550
¢years 1 or 550 pairs per year.
The combination of these two lines would be a single function that modeled the
population of breeding pairs from 1990 to 2006, but it would be defined in two pieces.
This is an example of a piecewise-defined function.
The notation for these functions is a large “left brace” indicating the equations it
groups are part of a single function. Using selected data points and techniques from
Section 1.4, we find equations that could represent each piece are p1t2 350t 3000
for 0 t 10 and p1t2 550t 1000 for t 7 10, where p(t) is the number of breeding pairs in year t. The complete function is then written:
function name
function pieces
350t 3000,
p1t2 e
550t 1000,
domain of each piece
2 t 10
t 7 10
In Figure 2.76, note that we indicated the exclusion of t 10 from the second piece of
the function using an open half-circle.
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Section 2.5 Piecewise-Defined Functions
EXAMPLE 1
䊳
Writing the Equation and Domain of a Piece wise-Defined Functio
The linear piece of the function shown has an equation
of y 2x 10. The equation of the quadratic
piece is y x2 9x 14.
10
a. Use the correct notation to write them as a
8
single piecewise-defined function and state the
domain of each piece by inspecting the graph.
6
b. State the range of the function.
Solution
䊳
y
f(x)
4
a. From the graph we note the linear portion is
defined between 0 and 3, with these endpoints
2
included as indicated by the closed dots. The
domain here is 0 x 3. The quadratic
0
portion begins at x 3 but does not include 3,
as indicated by the half-circle notation. The equation is
function name
f 1x2 e
function pieces
2x 10,
x2 9x 14,
(3, 4)
2
4
6
8
x
10
domain
0x3
3 6 x7
b. The largest y-value is 10 and the smallest is zero. The range is y 僆 30, 104 .
A. You’ve just seen how
we can state the equation,
domain, and range of a
piecewise-deﬁned function
from its graph
Now try Exercises 7 and 8
䊳
Piecewise-defined functions can be composed of more than two pieces, and can
involve functions of many kinds.
B. Graphing Piecewise-Defined Functions
As with other functions, piecewise-defined functions can be graphed by simply
plotting points. Careful attention must be paid to the domain of each piece, both to
evaluate the function correctly and to consider the inclusion/exclusion of endpoints. In
addition, try to keep the transformations of a basic function in mind, as this will often
help graph the function more efficiently.
EXAMPLE 2
䊳
Graphing a Piecewise-Defined Functio
Evaluate the piecewise-defined function by noting the effective domain of each piece,
then graph by plotting these points and using your knowledge of basic functions.
h1x2 e
Solution
䊳
x 2,
2 1x 1 1,
5 x 6 1
x 1
The first piece of h is a line with negative slope, while the second is a transformed
square root function. Using the endpoints of each domain specified and a few
additional points, we obtain the following:
For h1x2 x 2, 5 x 6 1,
x
h(x)
For h1x2 2 1x 1 1, x 1,
x
h(x)
5
3
1
1
3
1
0
1
1
(1)
3
3
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CHAPTER 2 More on Functions
After plotting the points from the first piece, we
connect them with a line segment noting the left
endpoint is included, while the right endpoint is
not (indicated using a semicircle around the
point). Then we plot the points from the second
piece and draw a square root graph, noting the
left endpoint here is included, and the graph
rises to the right. From the graph we note the
complete domain of h is x 僆 3 5, q 2 , and the
range is y 僆 3 1, q 2 .
h(x)
5
h(x) x 2
h(x) 2 x 1 1
5
5
x
5
Now try Exercises 9 through 12
䊳
Most graphing calculators are able to graph piecewise-defined functions. Consider
Example 3.
EXAMPLE 3
Solution
䊳
䊳
Graphing a Piecewise-Defined Function Using echnology
x 5,
5 x 6 2
Graph the function f 1x2 e
on a graphing calculator
2
1x 42 3, x 2
and evaluate f (2).
Figure 2.77
10
Both “pieces” are well known—the first is a line
with slope m 1 and y-intercept (0, 5). The second
is a parabola that opens upward, shifted 4 units to
the right and 3 units up. If we attempt to graph
10
f(x) using Y1 X 5 and Y2 1X 42 2 3 10
as they stand, the resulting graph may be
difficult to analyze because the pieces overlap
and intersect (Figure 2.77). To graph the functions
10
we must indicate the domain for each piece,
separated by a slash and enclosed in parentheses.
Figure 2.78
For instance, for the first piece we enter
Y1 X 5/1X 5 and X 6 22 , and for the
second, Y2 1X 42 2 3 1X 22 (Figure 2.78).
The slash looks like (is) the division symbol, but in
this context, the calculator interprets it as a means
of separating the function from the domain. The
inequality symbols are accessed using the 2nd
MATH (TEST) keys. As shown for Y , compound
1
inequalities must be entered in two parts, using the logical connector “and”: 2nd MATH
(LOGIC) 1:and. The graph is shown in Figure 2.79, where we see the function is
linear for x 僆 [5, 2) and quadratic for x 僆 [2, q ). Using the 2nd GRAPH (TABLE)
feature reveals the calculator will give an ERR: (ERROR) message for inputs outside
the domains of Y1 and Y2, and we see that f is defined for x 2 only for Y2: f 122 7
(Figure 2.80).
Figure 2.79
Figure 2.80
10
10
10
10
Now try Exercises 13 and 14
䊳
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Section 2.5 Piecewise-Defined Functions
As an alternative to plotting points, we can graph each piece of the function using
transformations of a basic graph, then erase those parts that are outside of the corresponding domain. Repeat this procedure for each piece of the function. One interesting and highly instructive aspect of these functions is the opportunity to investigate
restrictions on their domain and the ranges that result.
Piecewise and Continuous Functions
EXAMPLE 4
䊳
Graphing a Piecewise-Defined Functio
Graph the function and state its domain and range:
f 1x2 e
Solution
䊳
1x 32 2 12,
3,
0 6 x6
x 7 6
The first piece of f is a basic parabola, shifted three units right, reflected across the
x-axis (opening downward), and shifted 12 units up. The vertex is at (3, 12) and the
axis of symmetry is x 3, producing the following graphs.
1. Graph first piece of f
(Figure 2.81)
2. Erase portion outside domain.
of 0 6 x 6 (Figure 2.82).
Figure 2.81
Figure 2.82
y
y
12
y (x 3)2 12
12
10
10
8
8
6
6
4
4
2
2
1
1 2 3 4 5 6 7 8 9 10
x
y (x 3)2 12
1
1 2 3 4 5 6 7 8 9 10
x
The second function is simply a horizontal line through (0, 3).
3. Graph second piece of f
(Figure 2.83).
4. Erase portion outside domain
of x 7 6 (Figure 2.84).
Figure 2.83
Figure 2.84
y
12
y
y (x 3)2 12
12
10
10
8
8
6
6
4
y3
4
2
1
f (x)
2
1 2 3 4 5 6 7 8 9 10
x
1
1 2 3 4 5 6 7 8 9 10
x
The domain of f is x 僆 10, q 2, and the corresponding range is y 僆 3 3, 124.
Now try Exercises 15 through 18
䊳
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Piecewise and Discontinuous Functions
Notice that although the function in Example 4 was piecewise-defined, the graph was
actually continuous — we could draw the entire graph without lifting our pencil. Piecewise graphs also come in the discontinuous variety, which makes the domain and range
issues all the more important.
EXAMPLE 5
䊳
Graphing a Discontinuous Piecewise-Defined Functio
Graph g(x) and state the domain and range:
g1x2 e
Solution
䊳
12x 6,
x 6 10,
0x4
4 6 x9
The first piece of g is a line, with y-intercept (0, 6) and slope
1. Graph first piece of g
(Figure 2.85)
12.
¢y
¢x
2. Erase portion outside domain.
of 0 x 4 (Figure 2.86).
Figure 2.85
Figure 2.86
y
y
10
10
8
8
6
6
y qx 6
4
4
2
2
1
2
3
4
5
6
7
8
9 10
y qx 6
x
1
2
3
4
5
6
7
8
9 10
x
The second is an absolute value function, shifted right 6 units, reflected across
the x-axis, then shifted up 10 units.
WORTHY OF NOTE
As you graph piecewise-defined
functions, keep in mind that they
are functions and the end result
must pass the vertical line test. This
is especially important when we are
drawing each piece as a complete
graph, then erasing portions
outside the effective domain.
3. Graph second piece of g
(Figure 2.87).
4. Erase portion outside domain
of 4 6 x 9 (Figure 2.88).
Figure 2.87
Figure 2.88
y x 6 10
y
y
10
10
8
8
6
6
4
4
2
2
1
2
3
4
5
6
7
8
9 10
x
g(x)
1
2
3
4
5
6
7
8
9 10
x
Note that the left endpoint of the absolute value portion is not included
(this piece is not defined at x 4), signified by the open dot. The result is
a discontinuous graph, as there is no way to draw the graph other than by
“jumping” the pencil from where one piece ends to where the next begins.
Using a vertical boundary line, we note the domain of g includes all values
between 0 and 9 inclusive: x 僆 30, 9 4. Using a horizontal boundary line
shows the smallest y-value is 4 and the largest is 10, but no range values
exist between 6 and 7. The range is y 僆 34, 6 4 ´ 37, 10 4.
Now try Exercises 19 and 20
䊳
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Section 2.5 Piecewise-Defined Functions
EXAMPLE 6
䊳
Graphing a Discontinuous Function
The given piecewise-defined function is not continuous. Graph h(x) to see why,
then comment on what could be done to make it continuous.
x2 4
,
h1x2 • x 2
1,
Solution
䊳
x2
x2
The first piece of h is unfamiliar to us, so we elect to graph it by plotting points,
noting x 2 is outside the domain. This produces the table shown. After
connecting the points, the graph turns out to be a straight line, but with no
corresponding y-value for x 2. This leaves a “hole” in the graph at (2, 4), as
designated by the open dot (see Figure 2.89).
Figure 2.89
Figure 2.90
y
y
WORTHY OF NOTE
The discontinuity illustrated here is
called a removable discontinuity, as
the discontinuity can be removed
by redefining a single point on the
function. Note that after factoring
the first piece, the denominator is a
factor of the numerator, and writing
the result in lowest terms gives
h1x2 1x x221x2 22 x 2, x 2.
This is precisely the equation of the
line in Figure 2.89 3y x 24 .
x
h(x)
4
2
2
0
0
2
2
—
4
6
5
5
5
5
x
5
5
x
5
5
The second piece is pointwise-defined, and its graph is simply the point (2, 1)
shown in Figure 2.90. It’s interesting to note that while the domain of h is all real
numbers (h is defined at all points), the range is y 僆 1q, 42 ´ 14, q 2 as the
function never takes on the value y 4. In order for h to be continuous, we would
need to redefine the second piece as y 4 when x 2.
Now try Exercises 21 through 26
䊳
To develop these concepts more fully, it will help to practice finding the equation
of a piecewise-defined function given its graph, a process similar to that of Example 10
in Section 2.2.
EXAMPLE 7
䊳
Determining the Equation of a Piece wise-Defined Functio
y
Determine the equation of the piecewise-defined
function shown, including the domain for each piece.
Solution
䊳
By counting ¢y
¢x from (2, 5) to (1, 1), we find the
linear portion has slope m 2, and the y-intercept
must be (0, 1). The equation of the line is
y 2x 1. The second piece appears to be a
parabola with vertex (h, k) at (3, 5). Using this
vertex with the point (1, 1) in the general form
y a1x h2 2 k gives
y a1x h2 k
1 a11 32 2 5
4 a122 2
4 4a
1 a
2
5
4
6
5
general form, parabola is shifted right and up
substitute 1 for x, 1 for y, 3 for h, 5 for k
simplify; subtract 5
122 2 4
divide by 4
x
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CHAPTER 2 More on Functions
The equation of the parabola is y 1x 32 2 5. Considering the domains
shown in the figure, the equation of this piecewise-defined function must be
p1x2 e
2x 1,
1x 32 2 5,
B. You’ve just seen how
we can graph functions that
are piecewise-deﬁned
2 x 6 1
x1
Now try Exercises 27 through 30
䊳
C. Applications of Piecewise-Defined Functions
The number of applications for piecewise-defined functions is practically limitless. It
is actually fairly rare for a single function to accurately model a situation over a long
period of time. Laws change, spending habits change, and technology can bring abrupt
alterations in many areas of our lives. To accurately model these changes often requires
a piecewise-defined function.
EXAMPLE 8
䊳
Modeling with a Piecewise-Defined Functio
For the first half of the twentieth century, per capita spending on police protection
can be modeled by S1t2 0.54t 12, where S(t) represents per capita spending on
police protection in year t (1900 corresponds to year 0). After 1950, perhaps due to
the growth of American cities, this spending greatly increased: S1t2 3.65t 144.
Write these as a piecewise-defined function S(t), state the domain for each piece,
then graph the function. According to this model, how much was spent (per capita)
on police protection in 2000 and 2010? How much will be spent in 2014?
Source: Data taken from the Statistical Abstract of the United States for various years.
Solution
䊳
function name
S1t2 e
function pieces
effective domain
0.54t 12,
3.65t 144,
0 t 50
t 7 50
Since both pieces are linear, we can graph each part
using two points. For the first function, S102 12
and S1502 39. For the second function S1502 39
and S1802 148. The graph for each piece is shown
in the figure. Evaluating S at t 100:
S1t2 3.65t 144
S11002 3.6511002 144
365 144
221
S(t)
240
200
160
(80, 148)
120
80
40
0
(50, 39)
10 20 30 40 50 60 70 80 90 100 110 t
(1900 → 0)
About $221 per capita was spent on police protection in the year 2000. For 2010, the
model indicates that $257.50 per capita was spent: S11102 257.5. By 2014, this
function projects the amount spent will grow to S11142 272.1 or $272.10 per capita.
Now try Exercises 33 through 44
䊳
Step Functions
The last group of piecewise-defined functions we’ll explore are the step functions, so
called because the pieces of the function form a series of horizontal steps. These functions find frequent application in the way consumers are charged for services, and have
several applications in number theory. Perhaps the most common is called the greatest
integer function, though recently its alternative name, floor function, has gained
popularity (see Figure 2.91). This is in large part due to an improvement in notation
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171
Section 2.5 Piecewise-Defined Functions
and as a better contrast to ceiling functions. The floor function of a real number x, denoted f 1x2 :x ; or Œ x œ (we will use the first), is the largest integer less than or equal
to x. For instance, :5.9 ; 5, : 7; 7, and :3.4; 4.
In contrast, the ceiling function C1x2 <x = is the smallest integer greater than or
equal to x, meaning <5.9 = 6, <7 = 7, and <3.4 = 3 (see Figure 2.92). In simple terms, for any noninteger value on the number line, the floor function returns the
integer to the left, while the ceiling function returns the integer to the right. A graph of
each function is shown.
Figure 2.92
Figure 2.91
y
5
F(x) x
5
5
5
x
y C(x) x
5
5
5
x
5
One common application of floor functions is the price of theater admission, where
children 12 and under receive a discounted price. Right up until the day they’re 13, they
qualify for the lower price: :12364
365 ; 12. Applications of ceiling functions would
include how phone companies charge for the minutes used (charging the 12-min rate for
a phone call that only lasted 11.3 min: <11.3 = 12), and postage rates, as in Example 9.
EXAMPLE 9
䊳
Modeling Using a Step Function
In 2009 the first-class postage rate for large envelopes sent through the U.S. mail was
88¢ for the first ounce, then an additional 17¢ per ounce thereafter, up to 13 ounces.
Graph the function and state its domain and range. Use the graph to state the cost of
mailing a report weighing (a) 7.5 oz, (b) 8 oz, and (c) 8.1 oz in a large envelope.
䊳
The 88¢ charge applies to letters weighing between 0 oz and 1 oz. Zero is not
included since we have to mail something, but 1 is included since a large envelope
and its contents weighing exactly one ounce still costs 88¢. The graph will be a
horizontal line segment.
The function is defined for all
weights between 0 and 13 oz, excluding
zero and including 13: x 僆 10, 134 .
309
The range consists of single outputs
275
corresponding to the step intervals:
241
R 僆 588, 105, 122, p , 275, 2926.
a. The cost of mailing a 7.5-oz
report is 207¢.
b. The cost of mailing an 8.0-oz
report is still 207¢.
c. The cost of mailing an 8.1-oz
report is 207 17 224¢,
since this brings you up to the
next step.
C. You’ve just seen how
we can solve applications
involving piecewise-deﬁned
functions
Cost (¢)
Solution
207
173
139
105
71
1
2
3
4
5
6
7
8
9
10 11 12 13
Weight (oz)
Now try Exercises 45 through 48
䊳
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2–68
CHAPTER 2 More on Functions
2.5 EXERCISES
䊳
CONCEPTS AND VOCABULAR Y
Fill in each blank with the appropriate word or phrase. Carefully reread the section if needed.
1. A function whose entire graph can be drawn
without lifting your pencil is called a
function.
2. The input values for which each part of a piecewise
function is defined is the
of the function.
3. A graph is called
or jagged edges.
4. When graphing 2x 3 over a domain of x 7 0,
we leave an
dot at (0, 3).
if it has no sharp turns
5. Discuss/Explain how to determine if a piecewisedefined function is continuous, without having to
graph the function. Illustrate with an example.
䊳
6. Discuss/Explain how it is possible for the domain
of a function to be defined for all real numbers, but
have a range that is defined on more than one
interval. Construct an illustrative example.
DEVELOPING YOUR SKILLS
For Exercises 7 and 8, (a) use the correct notation to
write them as a single piecewise-defined function and
state the domain for each piece by inspecting the graph,
then (b) state the range of the function.
7. Y1 X2 6x 10; Y2 32X 52
y
12
10
8
2x 3
10. H1x2 • x2 1
5
x 6 0
0x 6 2
x 7 2
5
11. p1x2 • x2 4
2x 1
x 6 3
3 x 3
x 7 3
H132, H132 2, H10.0012, H112, H122, and H(3)
p152, p132, p122, p102, p132 , and p(5)
6
(5, 5)
4
2
2
4
6
8
10
12
x
8. Y1 1.5X 5 10; Y2 1X 7 5
x 3
12. q1x2 • 2
12x2 3x 2
x 6 1
1 x 6 2
x2
q132, q112, q102, q11.9992, q122 , and q(4)
y
12
Graph each piecewise-defined function using a graphing
calculator. Then evaluate each at x ⴝ 2 and x ⴝ 0.
10
8
6
(7, 5)
4
13. p1x2 e
x2
2x 4
6 x 2
x 7 2
14. q1x2 e
1x 4
x 2
4 x 0
0 6 x7
2
2
4
6
8
10
12 x
Evaluate each piecewise-defined function as indicated
(if possible).
2 x 6 2
9. h1x2 • x
2 x 6 3
5
x3
h152, h122, h112 2, h102, h12.9992, and h(3)
Graph each piecewise-defined function and state its
domain and range. Use transformations of the toolbox
functions where possible.
15. g1x2 e
1x 12 2 5
2x 12
1
x1
16. h1x2 e 2
1x 22 2 3
2 x 4
x 7 4
x0
0 6 x5
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17. H1x2 e
x 3
x 5 6
3
2x 1
18. w1x2 e
1x 32 2
x 3
19. f 1x2 • 9 x2
4
12x 1
20. h1x2 • x 5
3 1x 5
1
x1
21. p1x2 e 2
2
22. q1x2 e
1
2 1x
x3 1
25. f 1x2 • x 1
c
x 6 1
1x 6 9
x 6 2
2x6
x2 9
23. f 1x2 • x 3
c
27.
x4
x4
x 2
y
28.
f(x)
5
5
x3
x3
y
29.
5
5 x
x 3
5 x
5
y
30.
p(x)
5
5
g(x)
5
5
x 3
x2 3x 10
x5
24. f 1x2 •
c
x 2
Determine the equation of each piecewise-defined
function shown, including the domain for each piece.
Assume all pieces are toolbox functions.
x 6 3
3 x 5
x 7 5
2
x1
4x x
26. f 1x2 • x 2
c
x 6 3
3 x 6 2
x2
12 3 1
x1
3
Each of the following functions has a removable
discontinuity. Graph the first piece of each function,
then find the value of c so that a continuous function
results.
䊳
173
Section 2.5 Piecewise-Defined Functions
5 x
5
y
g(x)
5
5
5 x
5
x5
x5
WORKING WITH FORMULAS
31. Definition of absolute value: x ⴝ e
ⴚx
x
x⬍0
xⱖ0
The absolute value function can be stated as a
piecewise-defined function, a technique that is
sometimes useful in graphing variations of the
function or solving absolute value equations and
inequalities. How does this definition ensure that
the absolute value of a number is always positive?
Use this definition to help sketch the graph of
f 1x2 xx . Discuss what you notice.
32. Sand dune function:
ⴚx ⴚ 2 ⴙ 1 1 ⱕ x ⬍ 3
f 1x2 ⴝ •ⴚx ⴚ 4 ⴙ 1 3 ⱕ x ⬍ 5
ⴚx ⴚ 2k ⴙ 1 2k ⴚ 1 ⱕ x ⬍ 2k ⴙ1, for k 僆 N
There are a number of interesting graphs that can
be created using piecewise-defined functions, and
these functions have been the basis for more than
one piece of modern art. (a) Use the descriptive
name and the pieces given to graph the function f.
Is the function accurately named? (b) Use any
combination of the toolbox functions to explore
your own creativity by creating a piecewisedefined function with some interesting or appealing
characteristics. (c) For y x 2 1, solve for
x in terms of y.
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䊳
2–70
CHAPTER 2 More on Functions
APPLICATIONS
For Exercises 33 and 34, (a) write the information given as
a piecewise-defined function, and state the domain for each
piece by inspecting the graph. (b) Give the range of each.
where P(t) represents the percentage of households
owning stock in year t, with 1950 corresponding to
year 0.
0.03t2 1.28t 1.68
1.89t 43.5
0 t 30
t 7 30
S(t)
33. Results from advertising:
Due to heavy advertising,
initial sales of the Lynx
S(t)
Digital Camera grew very
rapidly, but started to
(5, 5)
decline once the advertising
blitz was over. During the
t
advertising campaign, sales
2
were modeled by the function S1t2 t 6t,
where S(t) represents hundreds of sales in month t.
However, as Lynx Inc. had hoped, the new product
secured a foothold in the market and sales leveled
out at a steady 500 sales per month.
P1t2 e
34. Decline of newspaper publishing: From the turn
of the twentieth century, the number of newspapers
(per thousand population) grew rapidly until the
1930s, when the growth slowed down and then
declined. The years 1940 to 1946 saw a “spike” in
growth, but the years 1947 to 1954 saw an almost
equal decline. Since 1954 the number has
continued to decline, but at a slower rate.
Source: 2004 Statistical Abstract of the United States, Table 1204; various
other years.
12
10
8
6
4
2
2
400
360
4
6
8
10
12
N(t)
(38, 328)
(54, 328)
320
(4, 238)
200
0
20
36. Dependence on foreign oil: America’s
dependency on foreign oil has always been a “hot”
political topic, with the amount of imported oil
fluctuating over the years due to political climate,
public awareness, the economy, and other factors.
The amount of crude oil imported can be
approximated by the function given, where A(t)
represents the number of barrels imported in year t
(in billions), with 1980 corresponding to year 0.
0.047t2 0.38t 1.9
A1t2 • 0.075t2 1.495t 5.265
0.133t 0.685
280
240
a. According to this model, what percentage of
American households held stock in the years
1955, 1965, 1975, 1985, and 1995? If this
pattern continues, what percentage held stock
in 2005? What percent will hold stock in
2015?
b. Why is there a discrepancy in the outputs of
each piece of the function for the year 1980
1t 302 ? According to how the function is
defined, which output should be used?
40
60
80
100
t (years since 1900)
The number of papers N per thousand population for
each period, respectively, can be approximated by
N1 1t2 0.13t2 8.1t 208,
N2 1t2 5.75t 46 374, and
N3 1t2 2.45t 460.
Source: Data from the Statistical Abstract of the United States, various years;
data from The First Measured Century, The AEI Press, Caplow, Hicks, and
Wattenberg, 2001.
35. Families that own stocks: The percentage of
American households that own publicly traded
stocks began rising in the early 1950s, peaked in
1970, then began to decline until 1980 when there
was a dramatic increase due to easy access over the
Internet, an improved economy, and other factors.
This phenomenon is modeled by the function P(t),
0t 6 8
8 t 11
t 7 11
a. Use A(t) to estimate the number of barrels
imported in the years 1983, 1989, 1995, and
2005. If this trend continues, how many barrels
will be imported in 2015?
b. What was the minimum number of barrels
imported between 1980 and 1988?
Source: 2004 Statistical Abstract of the United States, Table 897; various
other years.
37. Energy rationing: In certain areas of the United
States, power blackouts have forced some counties
to ration electricity. Suppose the cost is $0.09 per
kilowatt (kW) for the first 1000 kW a household
uses. After 1000 kW, the cost increases to 0.18 per
kW. (a) Write these charges for electricity in the
form of a piecewise-defined function C(h), where
C(h) is the cost for h kilowatt hours. Include the
domain for each piece. Then (b) sketch the graph
and determine the cost for 1200 kW.
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Section 2.5 Piecewise-Defined Functions
38. Water rationing: Many southwestern states have a
limited water supply, and some state governments try
to control consumption by manipulating the cost of
water usage. Suppose for the first 5000 gal a
household uses per month, the charge is $0.05 per
gallon. Once 5000 gal is used the charge doubles to
$0.10 per gallon. (a) Write these charges for water
usage in the form of a piecewise-defined function
C(w), where C(w) is the cost for w gallons of water.
Include the domain for each piece. Then (b) sketch
the graph and determine the cost to a household
that used 9500 gal of water during a very hot
summer month.
39. Pricing for natural gas: A local gas company
charges $0.75 per therm for natural gas, up to 25
therms. Once the 25 therms has been exceeded, the
charge doubles to $1.50 per therm due to limited
supply and great demand. (a) Write these charges
for natural gas consumption in the form of a
piecewise-defined function C(t), where C(t) is the
charge for t therms. Include the domain for each
piece. Then (b) sketch the graph and determine the
cost to a household that used 45 therms during a
very cold winter month.
40. Multiple births:
The number of
multiple births has
steadily increased
in the United
States during the
twentieth century
and beyond.
Between 1985 and
1995 the number
of twin births could be modeled by the function
T1x2 0.21x2 6.1x 52, where x is the
number of years since 1980 and T is in thousands.
After 1995, the incidence of twins becomes more
linear, with T1x2 4.53x 28.3 serving as a better
model. (a) Write the piecewise-defined function
modeling the incidence of twins for these years.
Include the domain of each piece. Then (b) sketch
the graph and use the function to estimate the
incidence of twins in 1990, 2000, and 2005. If this
trend continued, how many sets of twins were born
in 2010?
Source: National Vital Statistics Report, Vol. 50, No. 5, February 12, 2002
41. U.S. military expenditures: Except for the year
1991 when military spending was cut drastically, the
amount spent by the U.S. government on national
defense and veterans’ benefits rose steadily from
1980 to 1992. These expenditures can be modeled
by the function S1t2 1.35t2 31.9t 152,
where S(t) is in billions of dollars and 1980
corresponds to t 0.
175
From 1992 to 1996 this spending declined, then
began to rise in the following years. From 1992 to
2002, military-related spending can be modeled by
S1t2 2.5t2 80.6t 950.
Source: 2004 Statistical Abstract of the United States, Table 492
(a) Write S(t) as a single piecewise-defined
function. Include stating the domain for each piece.
Then (b) sketch the graph and use the function to
estimate the amount spent by the United States in
2005, 2008, and 2012 if this trend continues.
42. Amusement arcades: At a local amusement
center, the owner has the SkeeBall machines
programmed to reward very high scores. For scores
x
of 200 or less, the function T1x2 10
models the
number of tickets awarded (rounded to the nearest
whole). For scores over 200, the number of tickets
is modeled by T1x2 0.001x2 0.3x 40.
(a) Write these equation models of the number of
tickets awarded in the form of a piecewise-defined
function. Include the domain for each piece. Then
(b) sketch the graph and find the number of tickets
awarded to a person who scores 390 points.
43. Phone service charges: When it comes to phone
service, a large number of calling plans are
available. Under one plan, the first 30 min of any
phone call costs only 3.3¢ per minute. The charge
increases to 7¢ per minute thereafter. (a) Write this
information in the form of a piecewise-defined
function. Include the domain for each piece. Then
(b) sketch the graph and find the cost of a 46-min
phone call.
44. Overtime wages: Tara works on an assembly line,
putting together computer monitors. She is paid
$9.50 per hour for regular time (0, 40 hr], $14.25
for overtime (40, 48 hr], and when demand for
computers is high, $19.00 for double-overtime
(48, 84 hr]. (a) Write this information in the form
of a simplified piecewise-defined function. Include
the domain for each piece. (b) Then sketch the
graph and find the gross amount of Tara’s check for
the week she put in 54 hr.
45. Admission prices: At Wet Willy’s Water World,
infants under 2 are free, then admission is charged
according to age. Children 2 and older but less than
13 pay $2, teenagers 13 and older but less than 20
pay $5, adults 20 and older but less than 65 pay $7,
and senior citizens 65 and older get in at the
teenage rate. (a) Write this information in the form
of a piecewise-defined function. Include the
domain for each piece. Then (b) sketch the graph
and find the cost of admission for a family of nine
which includes: one grandparent (70), two adults
(44/45), 3 teenagers, 2 children, and one infant.
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46. Demographics: One common use of the floor
function y : x; is the reporting of ages. As of
2007, the record for longest living human is
122 yr, 164 days for the life of Jeanne Calment,
formerly of France. While she actually lived
x 122164
365 years, ages are normally reported
using the floor function, or the greatest integer
number of years less than or equal to the actual
age: :122164
365 ; 122 years. (a) Write a function
A(t) that gives a person’s age, where A(t) is the
reported age at time t. (b) State the domain of the
function (be sure to consider Madame Calment’s
record). Report the age of a person who has been
living for (c) 36 years; (d) 36 years, 364 days;
(e) 37 years; and (f) 37 years, 1 day.
47. Postage rates: The postal charge function from
Example 9 is simply a transformation of the basic
ceiling function y <x = . Using the ideas from
Section 2.2, (a) write the postal charges as a step
function C(w), where C(w) is the cost of mailing
a large envelope weighing w ounces, and (b) state
the domain of the function. Then use the function
to find the cost of mailing reports weighing:
(c) 0.7 oz, (d) 5.1 oz, (e) 5.9 oz; (f) 6 oz, and
(g) 6.1 oz.
䊳
2–72
CHAPTER 2 More on Functions
48. Cell phone charges: A national cell phone
company advertises that calls of 1 min or less do
not count toward monthly usage. Calls lasting
longer than 1 min are calculated normally using a
ceiling function, meaning a call of 1 min, 1 sec will
be counted as a 2-min call. Using the ideas from
Section 2.2, (a) write the cell phone charges as a
piecewise-defined function C(m), where C(m) is
the cost of a call lasting m minutes, and include the
domain of the function. Then (b) graph the
function, and (c) use the graph or function to
determine if a cell phone subscriber has exceeded
the 30 free minutes granted by her calling plan for
calls lasting 2 min 3 sec, 13 min 46 sec, 1 min 5
sec, 3 min 59 sec, and 8 min 2 sec. (d) What was
the actual usage in minutes and seconds?
49. Combined absolute value graphs: Carefully
graph the function h1x2 x 2 x 3 using a
table of values over the interval x 僆 35, 5 4. Is the
function continuous? Write this function in
piecewise-defined form and state the domain for
each piece.
50. Combined absolute value graphs: Carefully
graph the function H1x2 x 2 x 3 using
a table of values over the interval x 僆 35, 5 4. Is
the function continuous? Write this function in
piecewise-defined form and state the domain for
each piece.
EXTENDING THE CONCEPT
51. You’ve heard it said, “any number divided by itself
2
is one.” Consider the functions f 1x2 xx 2 , and
x 2
g1x2 x 2 . Are these functions continuous?
52. Find a linear function h(x) that will make the
function shown a continuous function. Be sure to
include its domain.
x2
f 1x2 • h1x2
2x 3
䊳
x 6 1
x 7 3
MAINTAINING YOUR SKILLS
53. (Appendix A.5) Solve:
30
3
.
1 2
x2
x 4
54. (Appendix A.5) Compute the following and write the
result in lowest terms:
x3 3x2 4x 12
# 2 2x 6 13x 62
x3
x 5x 6
55. (1.4) Find an equation of the line perpendicular to
3x 4y 8, and through the point (0, 2). Write
the result in slope-intercept form.
56. (Appendix A.6/1.1) For the figure shown, (a) use the
Pythagorean Theorem to find the length of the
missing side and (b) state the area of the triangular
side.
8 cm
12 cm
20 cm
x cm
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Precalculus—
2.6
Variation: The Toolbox Functions in Action
LEARNING OBJECTIVES
A study of direct and inverse variation offers perhaps our clearest view of how mathematics is used to model real-world phenomena. While the basis of our study is
elementary, involving only the toolbox functions, the applications are at the same
time elegant, powerful, and far reaching. In addition, these applications unite some of
the most important ideas in algebra, including functions, transformations, rates of
change, and graphical analysis, to name a few.
In Section 2.6 you will see
how we can:
A. Solve direct variations
B. Solve inverse variations
C. Solve joint variations
A. Toolbox Functions and Direct Variation
If a car gets 24 miles per gallon (mpg) of gas, we could express the
distance d it could travel as d ⫽ 24g. Table 2.4 verifies the distance
traveled by the car changes in direct or constant proportion to the
number of gallons used, and here we say, “distance traveled varies
directly with gallons used.” The equation d ⫽ 24g is called a direct
variation, and the coefficient 24 is called the constant of variation.
¢d
24
¢distance
⫽
⫽ , and we note
Using the rate of change notation,
¢gallons
¢g
1
this is actually a linear equation with slope m ⫽ 24. When working with
the constant k is preferred over m, and in general we have the following:
Table 2.4
g
d
1
24
2
48
3
72
4
96
variations,
Direct Variation
y varies directly with x, or y is directly proportional to x, if
there is a nonzero constant k such that
y ⫽ kx.
k is called the constant of variation
EXAMPLE 1
䊳
Writing a Variation Equation
Write the variation equation for these statements:
a. Wages earned varies directly with the number of hours worked.
b. The value of an office machine varies directly with time.
c. The circumference of a circle varies directly with the length of the diameter.
Solution
䊳
a. Wages varies directly with hours worked: W ⫽ kh
b. The Value of an office machine varies directly with time: V ⫽ kt
c. The Circumference varies directly with the diameter: C ⫽ kd
Now try Exercises 7 through 10
䊳
Once we determine the relationship between two variables is a direct variation, we try
to find the value of k and develop an equation model that can more generally be
applied. Note that “varies directly” indicates that one value is a constant multiple of the
other. In Example 1, you may have realized that if any one relationship between the
variables is known, we can solve for k by substitution. For instance, if the circumference of a circle is 314 cm when the diameter is 100 cm, C ⫽ kd becomes
314 ⫽ k11002 and division shows k ⫽ 3.14 (our estimate for ␲). The result is a formula for the circumference of any circle. This suggests the following procedure:
2–73
177
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Solving Applications of Variation
1. Translate the information given into an equation model, using k as the
constant of variation.
2. Substitute the first relationship (pair of values) given and solve for k.
3. Substitute this value for k in the original model to obtain the variation equation.
4. Use the variation equation to complete the application.
EXAMPLE 2
䊳
Solving an Application of Direct V ariation
The weight of an astronaut on the surface of another planet varies directly with
their weight on Earth. An astronaut weighing 140 lb on Earth weighs only 53.2 lb
on Mars. How much would a 170-lb astronaut weigh on Mars?
Solution
䊳
1. M ⫽ kE
“Mars weight varies directly with Earth weight”
2. 53.2 ⫽ k11402 substitute 53.2 for M and 140 for E
solve for k (constant of variation)
k ⫽ 0.38
Substitute this value of k in the original equation to obtain the variation equation,
then find the weight of a 170-lb astronaut that landed on Mars.
3. M ⫽ 0.38E
variation equation
4.
⫽ 0.3811702 substitute 170 for E
result
⫽ 64.6
An astronaut weighing 170 lb on Earth weighs only 64.6 lb on Mars.
Now try Exercises 11 through 14
䊳
The toolbox function from Example 2 was a line with slope k ⫽ 0.38, or k ⫽ 19
50 as
19
a fraction in simplest form. As a rate of change, k ⫽ ¢M
¢E ⫽ 50 , and we see that for every
50 additional pounds on Earth, the weight of an astronaut would increase by only 19 lb
on Mars.
EXAMPLE 3
䊳
Making Estimates from the Graph of a V ariation
The scientists at NASA are planning to send additional probes to the red planet
(Mars), that will weigh from 250 to 450 lb. Graph the variation equation from
Example 2, then use the graph to estimate the corresponding range of weights on
Mars. Check your estimate using the variation equation.
Solution
䊳
After selecting an appropriate scale, begin at (0, 0) and count off the slope
19
k ⫽ ¢M
¢E ⫽ 50 . This gives the points (50, 19), (100, 38), (200, 76), and so on.
From the graph (see dashed arrows), it
200
appears the weights corresponding to 250 lb
and 450 lb on Earth are near 95 lb and
150
170 lb on Mars. Using the equation gives
(300, 114)
100
variation equation
M ⫽ 0.38E
(100, 38)
⫽ 0.3812502 substitute 250 for E
50
⫽ 95,
(50, 19)
variation equation
M ⫽ 0.38E
0
100
200
300
400
500
⫽ 0.3814502 substitute 450 for E
Earth
⫽ 171, very close to our estimate from the graph.
Mars
178
Now try Exercises 15 and 16
䊳
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179
When toolbox functions are used to model variations, our knowledge of their graphs
and defining characteristics strengthens a contextual understanding of the application.
Consider Examples 4 and 5, where the squaring function is used.
EXAMPLE 4
䊳
Writing Variation Equations
Write the variation equation for these statements:
a. In free fall, the distance traveled by an object varies directly with the square of
the time.
b. The area of a circle varies directly with the square of its radius.
Solution
䊳
a. Distance varies directly with the square of the time: D ⫽ kt2.
b. Area varies directly with the square of the radius: A ⫽ kr2.
Now try Exercises 17 through 20
䊳
Both variations in Example 4 use the squaring function, where k represents the amount
of stretch or compression applied, and whether the graph will open upward or downward. However, regardless of the function used, the four-step solution process remains
the same.
EXAMPLE 5
䊳
Solving an Application of Direct V ariation
The range of a projectile varies directly with the square of its initial velocity. As
part of a circus act, Bailey the Human Bullet is shot out of a cannon with an initial
velocity of 80 feet per second (ft/sec), into a net 200 ft away.
a. Find the constant of variation and write the variation equation.
b. Graph the equation and use the graph to estimate how far away the net should
be placed if initial velocity is increased to 95 ft/sec.
c. Determine the accuracy of the estimate from (b) using the variation equation.
䊳
a. 1. R ⫽ kv2
“Range varies directly with the square of the velocity”
2. 200 ⫽ k1802 2
substitute 200 for R and 80 for v
k ⫽ 0.03125
solve for k (constant of variation)
3. R ⫽ 0.03125v2
variation equation (substitute 0.03125 for k )
b. Since velocity and distance are positive,
400
we again use only QI. The graph is a
(100, 313)
parabola that opens upward, with the
300
vertex at (0, 0). Selecting velocities
200
from 50 to 100 ft/sec, we have:
2
R ⫽ 0.03125v
variation equation
100
2
(50, 78)
⫽ 0.031251502 substitute 50 for v
result
⫽ 78.125
0
20
40
60
80
100
120
Velocity
Likewise substituting 100 for v gives
R ⫽ 312.5 ft. Scaling the axes and using
(0, 0), (50, 78), and (100, 313) produces the graph shown. At 95 ft/sec (dashed
lines), it appears the net should be placed about 280 ft away.
c. Using the variation equation gives:
4. R ⫽ 0.03125v2
variation equation
⫽ 0.031251952 2 substitute 95 for v
R ⫽ 282.03125
result
Our estimate was off by about 2 ft. The net should be placed about 282 ft away.
Distance
Solution
Now try Exercises 21 through 26
䊳
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We now have a complete picture of this relationship, in which the required information can be presented graphically (Figure 2.93), numerically (Figure 2.94), verbally,
and in equation form. This enables the people requiring the information, i.e., Bailey
himself (for obvious reasons) and the Circus Master who is responsible, to make more
informed (and safe) decisions.
Figure 2.93
Figure 2.94
400
120
0
⫺50
R = 0.03125v2
Range R varies as the
square of the velocity
A. You’ve just seen how
we can solve direct variations
Note: For Examples 7 and 8, the four steps of the solution process were used in
sequence, but not numbered.
B. Inverse Variation
Table 2.5
Price
(dollars)
Demand
(1000s)
8
288
9
144
10
96
11
72
12
57.6
Numerous studies have been done that relate the price of a commodity to the
demand — the willingness of a consumer to pay that price. For instance, if there is a
sudden increase in the price of a popular tool, hardware stores know there will be a
corresponding decrease in the demand for that tool. The question remains, “What is
this rate of decrease?” Can it be modeled by a linear function with a negative slope?
A parabola that opens downward? Some other function? Table 2.5 shows some
(simulated) data regarding price versus demand. It appears that a linear function is
not appropriate because the rate of change in the number of tools sold is not
constant. Likewise a quadratic model seems inappropriate, since we don’t expect
demand to suddenly start rising again as the price continues to increase. This
phenomenon is actually an example of inverse variation, modeled by a transformation of the reciprocal function y ⫽ kx. We will often rewrite the equation as y ⫽ k1 1x 2
to clearly see the inverse relationship. In the case at hand, we might write D ⫽ k1 P1 2,
where k is the constant of variation, D represents the demand for the product, and P
the price of the product. In words, we say that “demand varies inversely as the
price.” In other applications of inverse variation, one quantity may vary inversely as
the square of another [Example 6(b)], and in general we have
Inverse Variation
y varies inversely with x, or y is inversely proportional to x, if
there is a nonzero constant k such that
1
y ⫽ k a b.
x
k is called the constant of variation
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Section 2.6 Variation: The Toolbox Functions in Action
EXAMPLE 6
䊳
Writing Inverse Variation Equations
Write the variation equation for these statements:
a. In a closed container, pressure varies inversely with the volume of gas.
b. The intensity of light varies inversely with the square of the distance from the
source.
Solution
䊳
a. Pressure varies inversely with the Volume of gas: P ⫽ k1 V1 2.
b. Intensity of light varies inversely with the square of the distance: I ⫽ k a
1
b.
d2
Now try Exercises 27 through 30
EXAMPLE 7
䊳
䊳
Solving an Application of In verse Variation
Boyle’s law tells us that in a closed container with constant temperature, the
volume of a gas varies inversely with the pressure applied (see illustration).
Suppose the air pressure in a closed cylinder is 50 pounds per square inch (psi)
when the volume of the cylinder is 60 in3.
a. Find the constant of variation and write the variation equation.
b. Use the equation to find the volume, if the pressure is increased to 150 psi.
Solution
䊳
Illustration of Boyle's Law
volume
low
pressure
70
60
50
40
30
20
10
0
pressure
temp
50 psi
150°
volume
high
pressure
70
60
50
40
30
20
10
0
pressure
temp
150 psi
150°
B. You’ve just seen how
we can solve inverse variations
1
a. V ⫽ k a b
P
1
60 ⫽ k a b
50
k ⫽ 3000
“volume varies inversely with the pressure”
substitute 60 for V and 50 for P.
constant of variation
1
V ⫽ 3000 a b variation equation (substitute 3000 for k )
P
b. Using the variation equation we have:
1
variation equation
V ⫽ 3000 a b
P
1
b substitute 150 for P
⫽ 3000 a
150
⫽ 20
result
When the pressure is increased to 150 psi, the volume decreases to 20 in3.
Now try Exercises 31 through 34
䊳
Figure 2.95
As an application of the reciprocal function,
250
the relationship in Example 7 is easily graphed
1
as a transformation of y ⫽ . Using an approprix
ate scale and values in QI, only a vertical stretch
200
of 3000 is required and the result is shown in Fig- 0
ure 2.95. As noted, when the pressure increases
the volume decreases, or in notation: as P S q ,
V S 0. Applications of this sort can be as sophis⫺25
ticated as the manufacturing of industrial pumps
and synthetic materials, or as simple as cooking a homemade dinner. Simply based on
the equation, how much pressure is required to reduce the volume of gas to 1 in3?
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C. Joint or Combined Variations
Just as some decisions might be based
Figure 2.96
on many considerations, often the relationship between two variables depends
on a combination of factors. Imagine a
wooden plank laid across the banks of a
stream for hikers to cross the streambed
(see Figure 2.96). The amount of
weight the plank will support depends
on the type of wood, the width and height of the plank’s cross section, and the distance between the supported ends (see Exercises 59 and 60). This is an example of a
joint variation, which can combine any number of variables in different ways. Two
general possibilities are: (1) y varies jointly with the product of x and p: y ⫽ kxp; and
(2) y varies jointly with the product of x and p, and inversely with the square of q:
y ⫽ kxp1 q12 2 . For practice writing joint variations as an equation model, see Exercises
35 through 40.
EXAMPLE 8
䊳
Solving an Application of Joint V ariation
The amount of fuel used by a certain ship
traveling at a uniform speed varies jointly with
the distance it travels and the square of the
velocity. If 200 barrels of fuel are used to travel
10 mi at 20 nautical miles per hour, how far
does the ship travel on 500 barrels of fuel at
30 nautical miles per hour?
Solution
䊳
F ⫽ kdv2
200 ⫽ k1102 1202 2
200 ⫽ 4000k
0.05 ⫽ k
F ⫽ 0.05dv2
“Fuel use varies jointly with distance and velocity squared”
substitute 200 for F, 10 for d, and 20 for v
simplify and solve for k
constant of variation
equation of variation
To find the distance traveled at 30 nautical miles per hour using 500 barrels of fuel,
substitute 500 for F and 30 for v:
F ⫽ 0.05dv2
500 ⫽ 0.05d1302 2
500 ⫽ 45d
11.1 ⫽ d
equation of variation
substitute 500 for F and 30 for v
simplify
result
If 500 barrels of fuel are consumed while traveling 30 nautical miles per hour, the
ship covers a distance of just over 11 mi.
Now try Exercises 41 through 44
C. You’ve just seen how
we can solve joint variations
䊳
It’s interesting to note that the ship covers just over one additional mile, but
consumes 2.5 times the amount of fuel. The additional speed requires a great deal
more fuel.
There is a variety of additional applications in the Exercise Set. See Exercises 47
through 55.
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Section 2.6 Variation: The Toolbox Functions in Action
183
2.6 EXERCISES
䊳
CONCEPTS AND VOCABULAR Y
Fill in each blank with the appropriate word or phrase. Carefully reread the section if needed.
䊳
1. The phrase “y varies directly with x” is written
y ⫽ kx, where k is called the
of
variation.
2. If more than two quantities are related in a
variation equation, the result is called a
variation.
3. For a right circular cylinder, V ⫽ ␲r2h and we say,
the volume varies
with the
and the
of the radius.
4. The statement “y varies inversely with the square
of x” is written
.
5. Discuss/Explain the general procedure for solving
applications of variation. Include references to
keywords, and illustrate using an example.
6. The basic percent formula is amount equals
percent times base, or A ⫽ PB. In words, write this
out as a direct variation with B as the constant of
variation, then as an inverse variation with the
amount A as the constant of variation.
DEVELOPING YOUR SKILLS
Write the variation equation for each statement.
7. distance traveled varies directly with rate of speed
8. cost varies directly with the quantity purchased
9. force varies directly with acceleration
10. length of a spring varies directly with attached
weight
For Exercises 11 and 12, find the constant of variation
and write the variation equation. Then use the equation
to complete the table.
11. y varies directly with x; y ⫽ 0.6 when x ⫽ 24.
x
y
500
16.25
750
12. w varies directly with v; w ⫽ 13 when v ⫽ 5.
v
w
291
21.8
339
13. Wages and hours worked: Wages earned varies
directly with the number of hours worked. Last
week I worked 37.5 hr and my gross pay was
$344.25. Write the variation equation and
determine how much I will gross this week if I
work 35 hr. What does the value of k represent in
this case?
14. Pagecount and thickness of books: The thickness
of a paperback book varies directly as the number of
pages. A book 3.2 cm thick has 750 pages. Write the
variation equation and approximate the thickness of
Roget’s 21st Century Thesaurus (paperback—2nd
edition), which has 957 pages.
15. Building height and number of stairs: The
number of stairs in the stairwells of tall buildings
and other structures varies directly as the height of
the structure. The base and pedestal for the Statue
of Liberty are 47 m tall, with 192 stairs from
ground level to the observation deck at the top of
the pedestal (at the statue’s feet). (a) Find the
constant of variation and write the variation
equation, (b) graph the variation equation, (c) use
the graph to estimate the number of stairs from
ground level to the observation deck in the statue’s
crown 81 m above ground level, and (d) use the
equation to check this estimate. Was it close?
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16. Projected images: The height of a projected image
varies directly as the distance of the projector from
the screen. At a distance of 48 in., the image on the
screen is 16 in. high. (a) Find the constant of
variation and write the variation equation,
(b) graph the variation equation, (c) use the graph
to estimate the height of the image if the projector
is placed at a distance of 5 ft 3 in., and (d) use the
equation to check this estimate. Was it close?
Write the variation equation for each statement.
17. Surface area of a cube varies directly with the
square of a side.
18. Potential energy in a spring varies directly with the
square of the distance the spring is compressed.
19. Electric power varies directly with the square of
the current (amperes).
20. Manufacturing cost varies directly as the square of
the number of items made.
For Exercises 21 and 22, find the constant of variation
and write the variation equation. Then use the equation
to complete the table.
21. p varies directly with the square of q; p ⫽ 280
when q ⫽ 50
q
p
24. Geometry and geography: The area of an
equilateral triangle varies directly as the square of
one side. A triangle with sides of 50 yd has an area
of 1082.5 yd2. Find the area in mi2 of the region
bounded by straight lines connecting the cities of
Cincinnati, Ohio, Washington, D.C., and
Columbia, South Carolina, which are each
approximately 400 mi apart.
25. Galileo and gravity: The distance an object falls
varies directly as the square of the time it has been
falling. The cannonballs dropped by Galileo from
the Leaning Tower of Pisa fell about 169 ft in
3.25 sec. How long would it take a hammer,
accidentally dropped from a height of 196 ft by a
bridge repair crew, to splash into the water below?
According to the equation, if a camera accidentally
fell out of the News 4 Eye-in-the-Sky helicopter and
hit the ground in 2.75 sec, how high was the
helicopter?
26. Soap bubble surface area: When a child blows
small soap bubbles, they come out in the form of a
sphere because the surface tension in the soap
seeks to minimize the surface area. The surface
area of any sphere varies directly with the square
of its radius. A soap bubble with a 34 in. radius has a
surface area of approximately 7.07 in2. What is the
radius of a seventeenth-century cannonball that has
a surface area of 113.1 in2? What is the surface
area of an orange with a radius of 112 in.?
45
338.8
70
22. n varies directly with m squared; n ⫽ 24.75 when
m ⫽ 30
m
Write the variation equation for each statement.
27. The force of gravity varies inversely as the square
of the distance between objects.
28. Pressure varies inversely as the area over which it
is applied.
n
29. The safe load of a beam supported at both ends
varies inversely as its length.
99
30. The intensity of sound varies inversely as the
square of its distance from the source.
40
88
For Exercises 23 to 26, supply the relationship indicated
(a) in words, (b) in equation form, (c) graphically, and
(d) in table form, then (e) solve the application.
23. The Borg Collective: The surface area of a cube
varies directly as the square of one side. A cube
with sides of 14 13 cm has a surface area of
3528 cm2. Find the surface area in square meters of
the spaceships used by the Borg Collective in Star
Trek — The Next Generation, cubical spacecraft
with sides of 3036 m.
For Exercises 31 through 34, find the constant of
variation and write the variation equation. Then use the
equation to complete the table or solve the application.
31. Y varies inversely as the square of Z; Y ⫽ 1369
when Z ⫽ 3
Z
Y
37
2.25
111
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Section 2.6 Variation: The Toolbox Functions in Action
32. A varies inversely with B; A ⫽ 2450 when B ⫽ 0.8
B
A
140
6.125
560
33. Gravitational force: The effect of Earth’s gravity on
an object (its weight) varies inversely as the square of
its distance from the center of the planet (assume the
Earth’s radius is 6400 km). If the weight of an
astronaut is 75 kg on Earth (when r ⫽ 64002, what
would this weight be at an altitude of 1600 km above
the surface of the Earth?
34. Popular running shoes: The demand for a popular
new running shoe varies inversely with the price of
the shoes. When the wholesale price is set at $45,
the manufacturer ships 5500 orders per week to
retail outlets. Based on this information, how many
orders would be shipped per week if the wholesale
price rose to $55?
40. The electrical resistance in a wire varies directly
with its length and inversely as the cross-sectional
area of the wire.
For Exercises 41–44, find the constant of variation and
write the related variation equation. Then use the
equation to complete the table or solve the application.
41. C varies jointly with R and inversely with S
squared, and C ⫽ 21 when R ⫽ 7 and S ⫽ 1.5.
R
36. Horsepower varies jointly as the number of
cylinders in the engine and the square of the
cylinder’s diameter.
37. The area of a trapezoid varies jointly with its
height and the sum of the bases.
38. The area of a triangle varies jointly with its base
and its height.
39. The volume of metal in a circular coin varies
directly with the thickness of the coin and the
square of its radius.
䊳
S
C
120
22.5
200
12.5
15
10.5
42. J varies jointly with P and inversely with the square
root of Q, and J ⫽ 19 when P ⫽ 4 and Q ⫽ 25.
P
Q
47.5
112
J
118.75
31.36
44.89
Write the variation equation for each statement.
35. Interest earned varies jointly with the rate of
interest and the length of time on deposit.
66.5
43. Kinetic energy: Kinetic energy (energy attributed
to motion) varies jointly with the mass of the
object and the square of its velocity. Assuming a
unit mass of m ⫽ 1, an object with a velocity of
20 m per sec (m/s) has kinetic energy of 200 J.
How much energy is produced if the velocity is
increased to 35 m/s?
44. Safe load: The load that a horizontal beam can
support varies jointly as the width of the beam, the
square of its height, and inversely as the length of
the beam. A beam 4 in. wide and 8 in. tall can
safely support a load of 1 ton when the beam has a
length of 12 ft. How much could a similar beam
10 in. tall safely support?
WORKING WITH FORMULAS
3
45. Required interest rate: R(A) ⴝ 1
Aⴚ1
To determine the simple interest rate R that would be
required for each dollar ($1) left on deposit for 3 yr to
3
grow to an amount A, the formula R1A2 ⫽ 1
A⫺1
can be applied. (a) To what function family does this
formula belong? (b) Complete the table using a
calculator, then use the table to estimate the interest
rate required for each $1 to grow to $1.17.
(c) Compare your estimate to the value you get by
3
evaluating R(1.17). (d) For R ⫽ 1
A ⫺ 1, solve
for A in terms of R.
185
Amount A
1.0
1.05
1.10
1.15
1.20
1.25
Rate R
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46. Force between charged particles: F ⴝ k
Q1Q2
d2
The force between two charged particles is given by the formula shown, where F is the force (in joules — J), Q1
and Q2 represent the electrical charge on each particle (in coulombs — C), and d is the distance between them (in
meters). If the particles have a like charge, the force is repulsive; if the charges are unlike, the force is attractive.
(a) Write the variation equation in words. (b) Solve for k and use the formula to find the electrical constant k,
given F ⫽ 0.36 J, Q1 ⫽ 2 ⫻ 10 ⫺6 C, Q2 ⫽ 4 ⫻ 10 ⫺6 C, and d ⫽ 0.2 m. Express the result in scientific notation.
䊳
APPLICATIONS
Find the constant of variation “k” and write the
variation equation, then use the equation to solve.
costs $76.50, how much does a 24-ft spool of 38 -in.diameter tubing cost?
47. Cleanup time: The time required to pick up the
trash along a stretch of highway varies inversely
as the number of volunteers who are working. If
12 volunteers can do the cleanup in 4 hr, how many
volunteers are needed to complete the cleanup in
just 1.5 hr?
54. Electrical resistance: The electrical resistance of
a copper wire varies directly with its length and
inversely with the square of the diameter of the
wire. If a wire 30 m long with a diameter of 3 mm
has a resistance of 25 ⍀, find the resistance of a
wire 40 m long with a diameter of 3.5 mm.
48. Wind power: The wind farms in southern
California contain wind generators whose power
production varies directly with the cube of the
wind’s speed. If one such generator produces 1000 W
of power in a 25 mph wind, find the power it
generates in a 35 mph wind.
55. Volume of phone calls: The number of phone calls
per day between two cities varies directly as the
product of their populations and inversely as the
square of the distance between them. The city of
Tampa, Florida (pop. 300,000), is 430 mi from the
city of Atlanta, Georgia (pop. 420,000).
Telecommunications experts estimate there are
about 300 calls per day between the two cities. Use
this information to estimate the number of daily
phone calls between Amarillo, Texas (pop.
170,000), and Denver, Colorado (pop. 550,000),
which are also separated by a distance of about
430 mi. Note: Population figures are for the year
2000 and rounded to the nearest ten-thousand.
49. Pull of gravity: The weight of an object on the
moon varies directly with the weight of the object
on Earth. A 96-kg object on Earth would weigh only
16 kg on the moon. How much would a fully suited
250-kg astronaut weigh on the moon?
50. Period of a pendulum: The time that it takes for a
simple pendulum to complete one period (swing
over and back) varies directly as the square root of
its length. If a pendulum 20 ft long has a period of
5 sec, find the period of a pendulum 30 ft long.
51. Stopping distance: The stopping distance of an
automobile varies directly as the square root of its
speed when the brakes are applied. If a car requires
108 ft to stop from a speed of 25 mph, estimate the
stopping distance if the brakes were applied when
the car was traveling 45 mph.
52. Supply and demand: A chain of hardware stores
finds that the demand for a special power tool
varies inversely with the advertised price of the
tool. If the price is advertised at $85, there is a
monthly demand for 10,000 units at all
participating stores. Find the projected demand if
the price were lowered to $70.83.
53. Cost of copper tubing: The cost of copper tubing
varies jointly with the length and the diameter of
the tube. If a 36-ft spool of 14 -in.-diameter tubing
Source: 2005 World Almanac, p. 626.
56. Internet commerce: The likelihood of an eBay®
item being sold for its “Buy it Now®” price P, varies
directly with the feedback rating of the seller, and
P
, where MSRP
inversely with the cube of MSRP
represents the manufacturer’s suggested retail price.
A power eBay® seller with a feedback rating of
99.6%, knows she has a 60% likelihood of selling an
item at 90% of the MSRP. What is the likelihood a
seller with a 95.3% feedback rating can sell the
same item at 95% of the MSRP?
57. Volume of an egg: The volume of an egg laid by an
average chicken varies jointly with its length and the
square of its width. An egg measuring 2.50 cm wide
and 3.75 cm long has a volume of 12.27 cm3. A
Barret’s Blue Ribbon hen can lay an egg measuring
3.10 cm wide and 4.65 cm long. (a) What is the
volume of this egg? (b) As a percentage, how much
greater is this volume than that of an average
chicken’s egg?
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Section 2.6 Variation: The Toolbox Functions in Action
58. Athletic performance: Researchers have estimated
that a sprinter’s time in the 100-m dash varies
directly as the square root of her age and inversely
as the number of hours spent training each week. At
20 yr old, Gail trains 10 hr per week (hr/wk) and has
an average time of 11 sec. Assuming she continues
to train 10 hr/wk, (a) what will her average time be
at 30 yr old? (b) If she wants to keep her average
time at 11 sec, how many hours per week should she
train?
59. Maximum safe load: The maximum safe load M
that can be placed on a uniform horizontal beam
supported at both ends varies directly as the
width w and the square of the height h of the
beam’s cross section, and inversely as its length L
䊳
(width and height are assumed to be in inches,
and length in feet). (a) Write the variation
equation. (b) If a beam 18 in. wide, 2 in. high,
and 8 ft long can safely support 270 lb, what is
the safe load for a beam of like dimensions with
a length of 12 ft?
60. Maximum safe load: Suppose a 10-ft wooden
beam with dimensions 4 in. by 6 in. is made from
the same material as the beam in Exercise 59 (the
same k value can be used). (a) What is the maximum
safe load if the beam is placed so that width is 6 in.
and height is 4 in.? (b) What is the maximum safe
load if the beam is placed so that width is 4 in. and
height is 6 in.?
EXTENDING THE CONCEPT
61. The gravitational force F between two celestial
bodies varies jointly as the product of their masses
and inversely as the square of the distance d
between them. The relationship is modeled by
m m
Newton’s law of universal gravitation: F ⫽ k d1 2 2.
⫺11
Given that k ⫽ 6.67 ⫻ 10 , what is the
gravitational force exerted by a 1000-kg sphere on
another identical sphere that is 10 m away?
䊳
187
62. The intensity of light and sound both vary inversely
as the square of their distance from the source.
a. Suppose you’re relaxing one evening with a
copy of Twelfth Night (Shakespeare), and the
reading light is placed 5 ft from the surface of
the book. At what distance would the intensity
of the light be twice as great?
b. Tamino’s Aria (The Magic Flute — Mozart) is
playing in the background, with the speakers
12 ft away. At what distance from the speakers
would the intensity of sound be three times as
great?
MAINTAINING YOUR SKILLS
63. (Appendix A.2) Evaluate: a
2x4 ⫺2
b
3x3y
65. (2.4) State the domains of f and g given here:
x⫺3
a. f 1x2 ⫽ 2
x ⫺ 16
x⫺3
b. g1x2 ⫽
2x2 ⫺ 16
64. (Appendix A.4) Solve: x3 ⫹ 6x2 ⫹ 8x ⫽ 0.
66. (2.3) Graph by using transformations of the parent
function and plotting a minimum number of points:
f 1x2 ⫽ ⫺2冟x ⫺ 3冟 ⫹ 5.
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CHAPTER 2 More on Functions
MAKING CONNECTIONS
Making Connections: Graphically , Symbolically , Numerically, and V erbally
Eight graphs (a) through (h) are given. Match the characteristics shown in 1 through 16 to one of the eight graphs.
y
(a)
⫺5
y
(b)
5
⫺5
5 x
y
5 x
⫺5
5
⫺5
5 x
⫺5
y
(g)
5
5 x
⫺5
1. ____ domain: x 僆 1⫺q, 12 ´ 11, q 2
2. ____ y ⫽ 2x ⫹ 4 ⫺ 2
3. ____ f 1x2c for x 僆 11, q 2
4. ____ horizontal asymptote at y ⫽ ⫺1
1
⫹1
x⫹1
6. ____ domain: x 僆 3⫺4, 2 4
7. ____ y ⫽ 冟x ⫺ 1冟 ⫺ 4
5. ____ y ⫽
8. ____ f 1x2 ⱕ 0 for x 僆 31, q 2
y
(h)
5
⫺5
5 x
⫺5
⫺5
y
(f)
5
⫺5
⫺5
5 x
y
(d)
5
⫺5
⫺5
(e)
y
(c)
5
5 x
5
⫺5
⫺5
x
⫺5
9. ____ domain: x 僆 3⫺4, q 2
10. ____ f 1⫺32 ⫽ ⫺1, f 152 ⫽ 1
11. ____ basic function is shifted 3 units left,
reflected across x-axis, then shifted
up 2 units
12. ____ basic function is shifted 1 unit left,
2 units up
13. ____ f 1⫺32 ⫽ ⫺4, f 122 ⫽ 0
14. ____ as x S q , y S 1
15. ____ f 1x2 7 0 for x 僆 1⫺q, q 2
1x ⫹ 22 2 ⫺ 5,
16. ____ y ⫽ • 1
x ⫺ 1,
2
x 6 0
x ⱖ0
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Summary and Concept Review
189
SUMMAR Y AND CONCEPT REVIEW
SECTION 2.1
Analyzing the Graph of a Function
KEY CONCEPTS
• A function f is even (symmetric to the y-axis), if and only if when a point (x, y) is on the graph, then (⫺x, y) is also
on the graph. In function notation: f 1⫺x2 ⫽ f 1x2 .
• A function f is odd (symmetric to the origin), if and only if when a point (x, y) is on the graph, then (⫺x, ⫺y) is
also on the graph. In function notation: f 1⫺x2 ⫽ ⫺f 1x2 .
Intuitive descriptions of the characteristics of a graph are given here. The formal definitions can be found within
Section 2.1.
• A function is increasing in an interval if the graph rises from left to right (larger inputs produce larger outputs).
• A function is decreasing in an interval if the graph falls from left to right (larger inputs produce smaller outputs).
• A function is positive in an interval if the graph is above the x-axis in that interval.
• A function is negative in an interval if the graph is below the x-axis in that interval.
• A function is constant in an interval if the graph is parallel to the x-axis in that interval.
• A maximum value can be a local maximum, or global maximum. An endpoint maximum can occur at the
endpoints of the domain. Similar statements can be made for minimum values.
EXERCISES
State the domain and range for each function f (x) given. Then state the intervals where f is increasing or decreasing
and intervals where f is positive or negative. Assume all endpoints have integer values.
y
y
y
1.
2.
3.
5
10
10
⫺10
10 x
⫺5
5 x
⫺10
10 x
f(x)
⫺5
⫺10
⫺10
4. Determine whether the following are even 3 f 1⫺k2 ⫽ f 1k2 4 , odd 3 f 1⫺k2 ⫽ ⫺f 1k2 4 , or neither.
3
a. f 1x2 ⫽ 2x5 ⫺ 2x
c. p1x2 ⫽ 冟3x冟 ⫺ x3
3
1
x
x
x2 ⫺ 冟x冟
d. q1x2 ⫽
x
b. g1x2 ⫽ x4 ⫺
5. Draw the function f that has all of the following characteristics, then name the zeroes of the function and the
location of all local maximum and minimum values. [Hint: Write them in the form (c, f (c)).]
a. Domain: x 僆 3⫺6, 102
c. f 102 ⫽ 0
e. f 1x2c for x 僆 1⫺3, 32 ´ 17.5, 102
g. f 1x2 7 0 for x 僆 10, 62 ´ 19, 102
b. Range: y 僆 3⫺8, 62
d. f 1x2T for x 僆 1⫺6, ⫺32 ´ 13, 7.52
f. f 1x2 6 0 for x 僆 1⫺6, 02 ´ 16, 92
3
6. Use a graphing calculator to find the maximum and minimum values of f 1x2 ⫽ 2x5 ⫺ 1x. Round to the nearest
hundredth.
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CHAPTER 2 More on Functions
SECTION 2.2
The T oolbox Functions and T ransformations
KEY CONCEPTS
• The toolbox functions and graphs commonly used in mathematics are
• the identity function f 1x2 ⫽ x
• squaring function: f 1x2 ⫽ x2
• square root function: f 1x2 ⫽ 1x
• absolute value function: f 1x2 ⫽ 0 x 0
3
3
f
1x2
⫽
x
cubing
function:
•
• cube root function: f 1x2 ⫽ 1x
• For a basic or parent function y ⫽ f 1x2 , the general equation of the transformed function is y ⫽ af 1x ⫾ h2 ⫾ k.
For any function y ⫽ f 1x2 and h, k 7 0,
• the graph of y ⫽ f 1x2 ⫹ k is the graph
• the graph of y ⫽ f 1x2 ⫺ k is the graph
of y ⫽ f 1x2 shifted upward k units
of y ⫽ f 1x2 shifted downward k units
• the graph of y ⫽ f 1x ⫹ h2 is the graph of
• the graph of y ⫽ f 1x ⫺ h2 is the graph of
y ⫽ f 1x2 shifted left h units
y ⫽ f 1x2 shifted right h units
y
⫽
⫺f
1x2
the
graph
of
is
the
graph
of
the
graph of y ⫽ f 1⫺x2 is the graph of
•
•
y ⫽ f 1x2 reflected across the x-axis
y ⫽ f 1x2 reflected across the y-axis
• y ⫽ af 1x2 results in a vertical stretch
• y ⫽ af 1x2 results in a vertical compression
when a 7 1
when 0 6 a 6 1
Transformations
are
applied
in
the
following
order:
(1)
horizontal shifts, (2) reflections, (3) stretches or
•
compressions, and (4) vertical shifts.
EXERCISES
Identify the function family for each graph given, then (a) describe the end-behavior; (b) name the x- and y-intercepts;
(c) identify the vertex, initial point, or point of inflection (as applicable); and (d) state the domain and range.
y
y
y
7.
8.
9.
5
5
5
⫺5
⫺5
5 x
⫺5
5 x
⫺5
⫺5
10.
5 x
11.
y
5
⫺5
y
5
⫺5
5 x
5 x
⫺5
⫺5
Identify each function as belonging to the linear, quadratic, square root, cubic, cube root, or absolute value family.
Then sketch the graph using shifts of a parent function and a few characteristic points.
12. f 1x2 ⫽ ⫺1x ⫹ 22 2 ⫺ 5
13. f 1x2 ⫽ 2 0 x ⫹ 3 0
14. f 1x2 ⫽ x3 ⫺ 1
15. f 1x2 ⫽ 1x ⫺ 5 ⫹ 2
3
16. f 1x2 ⫽ 2x ⫹ 2
17. Apply the transformations indicated for the graph of f (x) given.
a. f 1x ⫺ 22
b. ⫺f 1x2 ⫹ 4
c. 12 f 1x2
y
5
(⫺4, 3)
⫺5
f(x)
(1, 3)
5 x
(⫺1.5, ⫺1)
⫺5
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SECTION 2.3
Summary and Concept Review
191
Absolute V alue Functions, Equations, and Inequalities
KEY CONCEPTS
• To solve absolute value equations and inequalities, begin by writing the equation in simplified form, with the
absolute value isolated on one side.
• If X and Y represent algebraic expressions and k is a nonnegative constant:
0 X 0 ⫽ k is equivalent to X ⫽ ⫺k or X ⫽ k
• Absolute value equations:
0 X 0 ⫽ 0 Y 0 is equivalent to X ⫽ Y or X ⫽ ⫺Y
0X 0 6 k is equivalent to ⫺k 6 X 6 k
• “Less than” inequalities:
• “Greater than” inequalities: 0 X 0 7 k is equivalent to X 6 ⫺k or X 7 k
These
properties also apply when the symbols “ⱕ” or “ⱖ”are used.
•
• If the absolute value quantity has been isolated on the left, the solution to a less-than inequality will be a single
interval, while the solution to a greater-than inequality will consist of two disjoint intervals.
• The multiplicative property states that for algebraic expressions A and B, 0 AB 0 ⫽ 0A 0 0 B 0 .
• Absolute value equations and inequalities can be solved graphically using the intersect method or the
zeroes/x-intercept method.
EXERCISES
Solve each equation or inequality. Write solutions to inequalities in interval notation.
18. 7 ⫽ 0 x ⫺ 3 0
19. ⫺2 0 x ⫹ 2 0 ⫽ ⫺10
20. 0 ⫺2x ⫹ 3 0 ⫽ 13
x
02x ⫹ 5 0
21.
22. ⫺3 0 x ⫹ 2 0 ⫺ 2 6 ⫺14
23. ` ⫺ 9 ` ⱕ 7
⫹8⫽9
3
2
24. 03x ⫹ 5 0 ⫽ ⫺4
25. 3 0x ⫹ 1 0 6 ⫺9
26. 2 0x ⫹ 1 0 7 ⫺4
0 3x ⫺ 2 0
27. 5 0 m ⫺ 2 0 ⫺ 12 ⱕ 8
28.
⫹ 6 ⱖ 10
2
29. Monthly rainfall received in Omaha, Nebraska, rarely varies by more than 1.7 in. from an average of 2.5 in. per
month. (a) Use this information to write an absolute value inequality model, then (b) solve the inequality to find
the highest and lowest amounts of monthly rainfall for this city.
SECTION 2.4
Basic Rational Functions and Power Functions; Mor e on the Domain
KEY CONCEPTS
• A rational function is one of the form V1x2 ⫽
p1x2
d1x2
, where p and d are polynomials and d1x2 ⫽ 0.
• The most basic rational functions are the reciprocal function f 1x2 ⫽ x and the reciprocal square function g1x2 ⫽ 2 .
x
• The line y ⫽ k is a horizontal asymptote of V if as 0 x 0 increases without bound, V(x) approaches k: as 0x 0 S q,
1
1
V1x2 S k.
• The line x ⫽ h is a vertical asymptote of V if as x approaches h, V(x) increases/decreases without bound: as x S h,
0V1x2 0 S q .
• The reciprocal and reciprocal square functions can be transformed using the same shifts, stretches, and reflections
as applied to other basic functions, with the asymptotes also shifted.
• A power function can be written in the form f 1x2 ⫽ x p where p is a constant real number and x is a variable.
1
1
n
If p ⫽ , where n is a natural number, f 1x2 ⫽ xn ⫽ 1x is called a root function in x.
n
m
• Given the rational exponent mn is in simplest form, the domain of f 1x2 ⫽ x n is 1⫺q, q 2 if n is odd, and 30, q2 if n
is even.
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CHAPTER 2 More on Functions
EXERCISES
Sketch the graph of each function using shifts of the parent function (not by using a table of values). Find and label the
x- and y-intercepts (if they exist) and redraw the asymptotes.
⫺1
1
30. f 1x2 ⫽
31. h1x2 ⫽
⫺1
⫺3
x⫹2
1x ⫺ 22 2
⫺7500
32. In a certain county, the cost to keep public roads free of trash is given by C1p2 ⫽
⫺ 75, where C(p)
p ⫺ 100
represents the cost (thousands of dollars) to keep p percent of the trash picked up. (a) Find the cost to pick up
30%, 50%, 70%, and 90% of the trash, and comment on the results. (b) Sketch the graph using the transformation
of a toolbox function. (c) Use mathematical notation to describe what happens if the county tries to keep 100% of
the trash picked up.
1
33. Use a graphing calculator to graph the functions f 1x2 ⫽ x1, g1x2 ⫽ x2, and h1x2 ⫽ x␲ in the same viewing window.
What is the domain of each function?
2␲ 32
r models the time T (in hr) it takes for a satellite to complete one revolution around
34. The expression T ⫽
37,840
the Earth, where r represents the radius (in km) of the orbit measured from the center of the Earth. If the Earth
has a radius of 6370 km, (a) how long does it takes for a satellite at a height of 200 km to complete one orbit?
(b) What is the orbital height of a satellite that completes one revolution in 4 days (96 hr)?
SECTION 2.5
Piecewise-Defined Functions
KEY CONCEPTS
• Each piece of a piecewise-defined function has a domain over which that piece is defined.
• To evaluate a piecewise-defined function, identify the domain interval containing the input value, then use the
piece of the function corresponding to this interval.
• To graph a piecewise-defined function you can plot points, or graph each piece in its entirety, then erase portions
of the graph outside the domain indicated for each piece.
• If the graph of a function can be drawn without lifting your pencil from the paper, the function is continuous.
• A discontinuity is said to be removable if we can redefine the function to “fill the hole.”
• Step functions are discontinuous and formed by a series of horizontal steps.
• The floor function : x; gives the largest integer less than or equal to x.
• The ceiling function < x = is the smallest integer greater than or equal to x.
EXERCISES
35. For the graph and functions given, (a) use the correct notation to write the relation as a
single piecewise-defined function, stating the effective domain for each piece by inspecting
the graph; and (b) state the range of the function: Y1 ⫽ 5, Y2 ⫽ ⫺X ⫹ 1,
Y3 ⫽ 3 1X ⫺ 3 ⫺ 1.
36. Use a table of values as needed to graph h(x), then state its domain and range. If the
function has a pointwise (removable) discontinuity, state how the second piece could be
redefined so that a continuous function results.
x2 ⫺ 2x ⫺ 15 x ⫽ ⫺3
,
x⫹3
h1x2 ⫽ •
⫺6,
x ⫽ ⫺3
37. Evaluate the piecewise-defined function p(x): p1⫺42, p1⫺22, p12.52, p12.992, p132 , and p13.52
⫺4,
x 6 ⫺2
⫺2 ⱕ x 6 3
p1x2 ⫽ • ⫺冟x冟 ⫺ 2,
31x ⫺ 9, x ⱖ 3
y
10
Y3
Y1
Y2
⫺10
10 x
⫺10
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Practice Test
193
38. Sketch the graph of the function and state its domain and range. Use transformations of the toolbox functions
where possible.
2 1⫺x ⫺ 3 ⫺ 4,
q1x2 ⫽ • ⫺2冟x冟 ⫹ 2,
21x ⫺ 3 ⫺ 4,
x ⱕ ⫺3
⫺3 6 x 6 3
xⱖ3
39. Many home improvement outlets now rent flatbed trucks in support of customers that purchase large items. The
cost is $20 per hour for the first 2 hr, $30 for the next 2 hr, then $40 for each hour afterward. Write this information
as a piecewise-defined function, then sketch its graph. What is the total cost to rent this truck for 5 hr?
Variation: The T oolbox Functions in Action
SECTION 2.6
KEY CONCEPTS
• Direct variation: If there is a nonzero constant k such that y ⫽ kx, we say, “y varies directly with x” or “y is
directly proportional to x” (k is called the constant of variation).
1
• Inverse variation: If there is a nonzero constant k such that y ⫽ k a x b we say, “y varies inversely with x” or y is
inversely proportional to x.
• In some cases, direct and inverse variations work simultaneously to form a joint variation.
• The process for solving variation applications can be found on page 178.
EXERCISES
Find the constant of variation and write the equation model, then use this model to complete the table.
40. y varies directly as the cube root of x;
41. z varies directly as v and inversely as the
y ⫽ 52.5 when x ⫽ 27.
square of w; z ⫽ 1.62 when w ⫽ 8 and
v ⫽ 144.
x
y
216
12.25
v
w
196
7
z
1.25
729
24
17.856
48
42. Given t varies jointly with u and v, and inversely as w, if t ⫽ 30 when u ⫽ 2, v ⫽ 3, and w ⫽ 5, find t when
u ⫽ 8, v ⫽ 12, and w ⫽ 15.
43. The time that it takes for a simple pendulum to complete one period (swing over and back) is directly proportional
to the square root of its length. If a pendulum 16 ft long has a period of 3 sec, find the time it takes for a 36-ft
pendulum to complete one period.
PRACTICE TEST
1. Determine the following from the graph shown.
a. the domain and range
b. estimate the value of f 1⫺12
c. interval(s) where f (x) is negative or positive
d. interval(s) where f (x) is increasing, decreasing, or constant.
e. an equation for f (x)
y
f(x)
5
4
3
2
1
⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
⫺5
1 2 3 4 5 x
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CHAPTER 2 More on Functions
12. After the engine is cut at t ⫽ 0, a boat coasts for a
while before stopping. The distance D it travels over
240
t sec can be modeled by D1t2 ⫽ 60 ⫺
. If
1t ⫹ 22 2
the boat comes to a complete stop after traveling 59 ft,
use a graphing calculator to determine the time
required to stop. Round your answer to the nearest
tenth.
For the function h(x) whose partial graph is given.
2. Complete the graph if h is known to be even.
3. Complete the graph if h is known to be odd.
y
5
⫺5
5 x
h(x)
⫺5
4. Use a graphing calculator to find the maximum and
minimum values of f 1x2 ⫽ 0 x2 ⫹ 4x ⫺ 11 0 ⫺ 7.
Round answers to nearest hundredth when necessary.
5. Each function graphed here is from a toolbox
function family. For each graph, (a) identify the
function family, (b) state the domain and range,
(c) identify x- and y-intercepts, (d) discuss the endbehavior, and (e) solve the inequalities f 1x2 7 0 and
f 1x2 6 0.
I.
II.
y
5
⫺5
⫺5
5 x
⫺5
III.
y
5
5 x
⫺5
y
IV.
5
⫺5
y
5
⫺5
5 x
⫺5
5 x
⫺5
Sketch each graph using a transformation.
6. f 1x2 ⫽ 0 x ⫺ 2 0 ⫹ 3
7. g1x2 ⫽ ⫺1x ⫹ 32 ⫺ 2
2
Solve each inequality. Write the solutions in interval
notation.
8.
2
0 3x ⫺ 1 0 7 14
3
9. 5 ⫺ 2 0 x ⫹ 2 0 ⱖ 1
10. Use a graphing calculator to solve the equation.
1.7 0 x ⫺ 0.75 0 ⫹ 3 ⫽ 3 ⫺
3
3
`x ⫺ `
5
4
2
11. Sketch the graph of f 1x2 ⫽
. Find and label the
x⫹3
x- and y-intercepts, if they exist, along with all
asymptotes.
13. Find the domains of the following functions.
2
5
a. f 1x2 ⫽ 2.09x 5
b. g1x2 ⫽ ⫺4.22x 2
c. h1t2 ⫽ 4.5t␲
14. Identify the vertical and horizontal asymptotes of
3
g1x2 ⫽
⫺ 1.
1x ⫹ 22 2
15. Using time-lapse photography,
Time
Size
the spread of a liquid is
(sec)
(mm)
tracked in one-fifth of a
0.2
0.39
second intervals, as a small
0.4
1.27
amount of liquid is dropped on
0.6
3.90
a piece of fabric. A power
function provides a reasonable
0.8
10.60
model for the first second.
1
21.50
Use a graphing calculator to
(a) graph a scatterplot of the data and (b) find an
equation model using a power regression (round to
two decimal places). Use the equation to estimate
(c) the size of the stain after 0.5 sec and (d) how
long it will take the stain to reach a size of 15 mm.
16. The following function has two removable
discontinuities. Find the values of a and b so that a
continuous function results.
x3 ⫹ x2 ⫺ 4x ⫺ 4
,
x2 ⫺ x ⫺ 2
g1x2 ⫽ μ
a,
b,
x ⫽ ⫺1, 2
x ⫽ ⫺1
x⫽2
17. The annual output of a wind turbine varies jointly
with the square of the blade diameter and the cube of
the average wind speed. If a 10-ft-diameter turbine
in 12 mph average winds produces 2300 KWH/year,
how much will a 6 ft-diameter turbine produce in
15 mph average winds? Round to the nearest
KWH/year.
4,
18. Given h1x2 ⫽ • 2x,
x2,
x 6 ⫺2
⫺2 ⱕ x ⱕ 2
x 7 2
a. Find h1⫺32 , h1⫺22 , and h1 52 2
b. Sketch the graph of h. Label important points.
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Calculator Exploration and Discovery
19. By observing a significantly smaller object orbiting a
large celestial body, astronomers can easily determine
the mass of the larger. Appealing to Kepler’s third law
of planetary motion, we know the mass of the large
body varies directly with the cube of the mean
distance to the smaller and inversely with the square
of its orbital period. Write the variation equation.
Using the mean Earth/Sun distance of 1.496 ⫻ 108 km
and the Earth’s orbital period of 1 yr, the mass of the
Sun has been calculated to be 1.98892 ⫻ 1030 kg.
Given the orbital period of Mars is 1.88 yr, find its
mean distance from the Sun.
195
20. The maximum load that can be supported by a
rectangular beam varies jointly with its width and
its height squared and inversely with its length. If a
beam 10 ft long, 3 in. wide, and 4 in. high can
support 624 lb, how many pounds could a 12-ft-long
beam with the same dimensions support?
CALCULATOR EXPLORA TION AND DISCOVER Y
Studying Joint V ariations
Although a graphing calculator is limited to displaying the relationship between only two variables (for the most part),
it has a feature that enables us to see how these two are related with respect to a third. Consider the variation equation
from Example 8 in Section 2.6: F ⫽ 0.05dv2. If we want to investigate the relationship between fuel consumption and
velocity, we can have the calculator display multiple versions of the relationship simultaneously for different values of d.
This is accomplished using the “{” and “}” symbols, which are 2nd functions to the parentheses. When the calculator
sees values between these grouping symbols and separated by commas, it is programmed to use each value independently
of the others, graphing or evaluating the relation for each value in the set. We illustrate by graphing the relationship
f ⫽ 0.05dv2 for three different values of d. Enter the equation on the Y= screen as Y1 ⫽ 0.05510, 20, 306X2, which
tells the calculator to graph the equations Y1 ⫽ 0.051102X2, Y1 ⫽ 0.051202X2, and Y1 ⫽ 0.051302X2 on the same grid.
Note that since d is constant, each graph is a parabola. Set the viewing window
Figure 2.97
using the values given in Example 8 as a guide. The result is the graph shown in
800
Figure 2.97, where we can study the relationship between these three variables
using the up
and down
arrows. From our work with the toolbox functions
and transformations, we know the widest parabola used the coefficient “10,” while
the narrowest parabola used the coefficient “30.” As shown, the graph tells us that
30
at a speed of 15 nautical miles per hour 1X ⫽ 152 , it will take 112.5 barrels of fuel 0
to travel 10 mi (the first number in the list). After pressing the
key, the cursor
jumps to the second curve, which shows values of X ⫽ 15 and Y ⫽ 225. This
means at 15 nautical miles per hour, it would take 225 barrels of fuel to travel 20
0
mi. Use these ideas to complete the following exercises:
Exercise 1: The comparison of distance covered versus fuel consumption at different speeds also makes an interesting
study. This time velocities are constant values and the distance varies. On the Y= screen, enter Y1 ⫽ 0.05x 510, 20, 3062.
What family of equations results? Use the up/down arrow keys for x ⫽ 15 (a distance of 15 mi) to find how many
barrels of fuel it takes to travel 15 mi at 10 mph, 15 mi at 20 mph, and 15 mi at 30 mph. Comment on what you notice.
Exercise 2: The maximum safe load S for a wooden horizontal plank supported at both ends varies jointly with the
width W of the beam, the square of its thickness T, and inversely with its length L. A plank 10 ft long, 12 in. wide, and
1 in. thick will safely support 450 lb. Find the value of k and write the variation equation, then use the equation to
explore:
a. Safe load versus thickness for a constant width and given lengths (quadratic function). Use w ⫽ 8 in. and {8, 12, 16}
for L.
b. Safe load versus length for a constant width and given thickness (reciprocal functional). Use w ⫽ 8 in. and
5 14, 12, 34 6 for thickness.
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CHAPTER 2 More on Functions
STRENGTHENING CORE SKILLS
Variation and Power Functions: y ⫽ kx p
You may have noticed that applications of power functions (Section 2.4) can also be stated as variations (Section 2.6):
From the general equation shown in the title of this feature, “... y varies directly as x to the p power.” Due to the
nature of real data and data collection, applications of power functions based on regression yield values of k (the
constant of variation) and p (the power) that cannot be written in exact form. However, “fixed” relationships modeled
by power functions produce values of k and p that can be written in exact form. For instance, the power function that
models planetary orbits states: The3 time T it takes a planet to complete one orbit varies directly with its orbital radius
to the three-halves power: T ⫽ kR2 . Here, the power is exactly 32 and the constant of variation turns out to be exactly 1
(also see Section 2.4, Exercise 78). Many times, finding this constant takes more effort, and utilizes the skills
developed in this and previous chapters. Consider the following.
Illustration 1 䊳 The volume V of a sphere varies directly with its surface area S to the three-halves power. If the
volume is approximately 33.51 cm3 when the surface area is 50.30 cm2, (a) find the constant of variation yielded by
these values (round to two decimal places), and (b) find the exact constant of variation dictated by the geometry of the
sphere and write the variation equation.
3
V ⫽ kS 2
3
33.51 ⫽ k150.302 2
33.51
3 ⫽ k
150.302 2
Solution 䊳 a.
0.09 ⬇ k
variation equation
substitute 33.51 for V, 50.30 for S
solve for k
approximate value for k
3
2
This gives V ⬇ 0.09S as an approximate relationship.
b. To find the true constant of variation fixed by the nature of spheres, we begin with the same set up, but substitute
the actual formulas for volume and surface area, then simplify.
3
V ⫽ kS 2
3
4 3
␲r ⫽ k14␲r 2 2 2
3
3
4 3
␲r ⫽ 8␲ 2 r3k
3
3
␲ ⫽ 6␲ 2k
␲
⫽k
3
6␲ 2
1
⫽k
1
6␲ 2
The constant of variation for this relationship is
variation equation
4
substitute ␲r3 for V, 4␲r 2 for S
3
3
properties of exponents: 42 ⫽ 8
3
multiply by , divide by r 3
4
solve for k
simplify (exact form)
3
1
1
1
S 2. Note that
⬇ 0.09.
, giving a variation equation of V ⫽
6 1␲
6 1␲
61␲
Studies of this type are important, because as the radius of the sphere gets larger, so does the error generated
by using
3/2
an approximate value. Using a radius of r ⫽ 18 cm with the approximate relationship 3V ⬇ 0.09 14␲182 2 4 , gives a
volume of near 23,381.6 cm3, while the volume found using the exact value for k is about 24,429.0 cm3.
Exercise 1: Use this Strengthening Core Skills feature to find the exact constant of variation for the following
relationship: The volume of a cube varies directly with its surface area to the three-halves power.
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Cumulative Review Chapters 1–2
197
CUMULATIVE REVIEW CHAPTERS 1–2
1. Given f 1x2 ⫽ 2x3 ⫹ 4x2 ⫹ 8x ⫺ 7,
1
find f 1⫺22 and f a b.
2
14. The graph of a function h(x) is shown. (a) State the
domain and estimate the range of h. (b) What are
the zeroes of the function? (c) What is the value
of h1⫺12 ? (d) If h1k2 ⫽ 9 what is the value of k?
2. Find the solution set for: 2 ⫺ x 6 5 and
3x ⫹ 2 6 8.
y
10
3. The area of a circle is 69 cm2. Find the
circumference of the same circle.
(⫺4, 0)
⫺10
4. The surface area of a cylinder is A ⫽ 2␲r ⫹ 2␲rh.
Write r in terms of A and h (solve for r).
2
5. Solve for x: ⫺213 ⫺ x2 ⫹ 5x ⫽ 41x ⫹ 12 ⫺ 7.
⫺10
⫺2
27 3
6. Evaluate without using a calculator: a b .
8
7. Find the slope of each line:
a. through the points: 1⫺4, 72 and (2, 5).
b. the line with equation 3x ⫺ 5y ⫽ 20.
8. Graph using transformations of a parent function.
a. f 1x2 ⫽ 1x ⫺ 2 ⫹ 3.
b. f 1x2 ⫽ ⫺ 0x ⫹ 2 0 ⫺ 3.
9. Graph the line passing through 1⫺3, 22 with a slope
of m ⫽ 12, then state its equation.
10. Find (a) the length of the hypotenuse and (b) the
perimeter of the triangle shown.
15. Add the rational expressions:
1
⫺2
⫹
a. 2
x
⫹
2
x ⫺ 3x ⫺ 10
2
c
b
b. 2 ⫺
a
4a
16. Simplify the radical expressions:
1
⫺10 ⫹ 172
a.
b.
4
12
17. Perform the division by factoring the numerator:
1x3 ⫺ 5x2 ⫹ 2x ⫺ 102 ⫼ 1x ⫺ 52.
18. Determine if the following relation is a function.
If not, how is the definition of a function violated?
57 cm
Titian
Raphael
176 cm
Giorgione
⫺1
⫹ 3 using a
11. Sketch the graph of h1x2 ⫽
1x ⫺ 12 2
transformation of the parent function.
12. Graph by plotting the y-intercept, then counting
10 x
¢y
¢x
to find additional points: y ⫽ 13x ⫺ 2
13. Graph the piecewise-defined function
x2 ⫺ 4, x 6 2
and determine
f 1x2 ⫽ e
x ⫺ 1,
2ⱕxⱕ8
the following:
a. the domain and range
b. the value of f 1⫺32, f 1⫺12, f 112, f 122, and f (3)
c. the zeroes of the function
d. interval(s) where f (x) is negative/positive
e. location of any local max/min values
f. interval(s) where f (x) is increasing/decreasing
da Vinci
Correggio
Parnassus
La Giocanda
The School of Athens
Jupiter and Io
Venus of Urbino
The Tempest
19. Find the center and radius of the circle defined by
x2 ⫹ 6x ⫹ y2 ⫺ 12y ⫹ 36 ⫽ 0.
20. The amount of pressure (in pounds per square
inch—psi) felt by a professional pearl diver as she
dives to harvest oysters, is 14.7 more than 0.43 times
the depth of the dive (in feet). Write the equation
model for this situation. If the oyster bed is at a
depth of 60 ft, how much pressure is felt?
21. The National Geographic Atlas of the World is a very
large, rectangular book with an almost inexhaustible
panoply of information about the world we live in.
The length of the front cover is 16 cm more than its
width, and the area of the cover is 1457 cm2. Use this
information to write an equation model, then use the
quadratic formula to determine the length and width
of the Atlas.
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CHAPTER 2 More on Functions
22. During a table tennis tournament, the championship
game between J.W. and Mike took a dramatic and
unexpected turn. At one point in the game, J.W.
was losing 5–15. Facing a crushing loss, he
summoned all his willpower and battled on to
a 21–19 victory! Assuming the game score
relationship is linear, find the slope of the line
between these two scores and discuss its meaning
in this context.
28. Use a graphing calculator and the intersectionof-graphs method to solve the inequality.
0 1.21x ⫺ 0.52 0 6 0.4x ⫹ 1.4
23. Solve by factoring:
a. 6x2 ⫺ 7x ⫽ 20
b. x3 ⫹ 5x2 ⫺ 15 ⫽ 3x
30. The data given shows the growth of the total U.S.
National Debt (in billions) for the years 1993 to
1999 11993 S 12 , and for the years 2001 to 2007
12001 S 12 , for each set of data, enter the data into a
graphing calculator, then
24. A theorem from elementary
geometry states, “A line
tangent to a circle is
perpendicular to the radius at
the point of tangency.” Find
the equation of the tangent
line for the circle and radius
shown.
y
5
4
3
2
1
(1, 2)
(⫺1, 1)
⫺5⫺4⫺3⫺2⫺1
⫺1
⫺2
⫺3
⫺4
⫺5
29. Graph the following piecewise-defined function
using a graphing calculator. Then use the TRACE
command to evaluate the function at x ⫽ 1.2.
⫺x ⫹ 2
⫺5 ⱕ x 6 ⫺2
f 1x2 ⫽ e
2
1x ⫺ 22 ⫺ 3 x ⱖ 1
Year
(scaled)
1993 to
1999
2001 to
2007
1
4.5
5.9
2
4.8
6.4
3
5.0
7.0
4
5.3
7.6
5
5.5
8.2
6
5.6
8.7
7
5.8
9.2
1 2 3 4 5 x
25. A triangle has its vertices at 1⫺4, 52, 14, ⫺12,
and (0, 8). Find the perimeter of the triangle
and determine whether or not it is a right
triangle.
Exercises 26 through 30 require the use of a graphing
calculator.
26. Use the zeroes method to solve the equation
2.71x ⫺ 32 ⫹ 0.3 ⫽ 1.8 ⫺ 1.21x ⫹ 42. Round your
answer to two decimal places.
27. Use a graphing calculator to graph the circle defined
by 1x ⫹ 22 2 ⫹ y2 ⫽ 4.
a. Set an appropriate window for viewing the
scatterplots, and determine if the associations are
linear or nonlinear.
b. If linear, find the regression equation for each
data set and graph both (as Y1 and Y2) in the same
window (round to two decimal places).
c. During which 7-year period did the national debt
increase faster? How much faster?
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Precalculus—
CONNECTIONS TO CALCULUS
Chapter 2 actually highlights numerous concepts and skills that transfer directly into a
study of calculus. In the Connections to Calculus introduction (page 105), we noted
that analyzing very small differences is one such skill, with this task carried out using
the absolute value concept. The ability to solve a wide variety of equation types will
also be a factor of your success in calculus. Here we’ll explore how these concepts and
skills are “connected.”
Solving Various Types of Equations
The need to solve equations of various types occurs frequently in both differential and
integral calculus, and the required skills will span a broad range of your algebraic experience. Here we’ll solve a type of radical equation that occurs frequently in a study
of optimization [finding the maximum or minimum value(s) of a function].
EXAMPLE 1
䊳
Minimizing Response Time
A boater is 70 yd away from a straight shoreline when she gets an emergency call
from her home, 400 yd downshore. Knowing she can row at 200 yd/min and run at
300 yd/min, how far downshore should she land the boat to make it home in the
shortest time possible?
Solution
䊳
As with other forms of problem solving, drawing an accurate sketch is an
important first step.
x
400 ⫺ x
Run
Home
70 yd
Row
Boat
From the diagram, we note the rowing distance will be 2x2 ⫹ 4900 (using the
Pythagorean theorem), and the running distance will be 400 ⫺ x (total minus
distance downshore).
distance
, we find the total time required to reach
rate
2x2 ⫹ 4900
400 ⫺ x
⫹
home is t1x2 ⫽
. Using the tools of calculus it can be
200
300
shown that the distance x downshore that results in the shortest possible time,
1
x
⫺
is a zero of T1x2 ⫽
. Find the zero(es) of T(x) and state the
300
200 2x2 ⫹ 4900
result in both exact and approximate form.
From the relationship time ⫽
2–95
199
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Connections to Calculus
Solution
䊳
Begin by isolating the radical on one side.
x
200 2x ⫹ 4900
x
2
⫺
1
⫽0
300
⫽
t ⬘( x ) ⫽ 0
1
300
200 2x ⫹ 4900
300x ⫽ 200 2x2 ⫹ 4900
1.5x ⫽ 2x2 ⫹ 4900
2.25x2 ⫽ x2 ⫹ 4900
1.25x2 ⫽ 4900
x2 ⫽ 3920
x ⫽ 13920
x ⫽ 28 15
⬇ 62.6
2
add
1
300
clear denominators
divide by 200
square both sides
subtract x 2
divide by 1.25
solve for x ; x 7 0 (distance)
simplify radical (exact form)
approximate form
The boater should row to a spot about 63 yd downshore,
then run the remaining 337 yd.
Now try Exercises 1 and 2
䊳
In addition to radical equations, equations involving rational exponents are often seen
in a study of calculus. Many times, solving these equations involves combining the
basic properties of exponents with other familiar skills such as factoring, or in this
case, factoring least powers.
EXAMPLE 2
䊳
Modeling the Motion of a P article
Suppose the motion of an object floating in turbulent water is modeled by the
function d1t2 ⫽ 1t 1t2 ⫺ 9t ⫹ 222, where d(t) represents the displacement (in
meters) at t sec. Using the tools of calculus, it can be shown that the velocity v of
1
5 3
27 1
the particle is given by v1t2 ⫽ t2 ⫺ t2 ⫹ 11t⫺2 . Find any time(s) t when the
2
2
particle is motionless 1v ⫽ 02.
Solution
䊳
Set the equation equal to zero and factor out the fraction and least power.
4
1
1
5t 2 a bt⫺2
2
1
5 32
27 1
t ⫺ t2 ⫹ 11t⫺2 ⫽ 0
2
2
2
1
1
1
1
⫺ 27t2 a bt⫺2 ⫹ 22a b t⫺2 ⫽ 0
2
2
1 ⫺12 2
t 15t ⫺ 27t ⫹ 222 ⫽ 0
2
1 ⫺12
t 15t ⫺ 222 1t ⫺ 12 ⫽ 0
2
1
22
t⫺2 ⫽ 0; t ⫽
or t ⫽ 1
5
original equation
rewrite to help factor
1 ⫺12
t (least power)
2
common factor
factor the trinomial
result
The particle is temporarily motionless at t ⫽ 4.4 sec and t ⫽ 1 sec.
Now try Exercises 3 and 4
䊳
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Connections to Calculus
201
Absolute Value Inequalities and Delta/Epsilon Form
While the terms may mean little to you now, the concept of absolute value plays an important role in the precise definition of a limit, intervals of convergence, and
derivatives. In the case of limits, the study of calculus concerns itself with very small
differences, as in the difference between the number 3 itself, and a number very close
x2 ⫺ 9
to 3. Consider the function f 1x2 ⫽
. From the implicit domain and the figures
x⫺3
shown, we see that f 1x2 (shown as Y1) is not defined at 3, but is defined for any
number near 3.
The figures also suggest that when x is a number very close to 3, f (x) is a number very
close to 6. Alternatively, we might say, “if the difference between x and 3 is very small,
the difference between f (x) and 6 is very small.” The most convenient way to express
this idea and make it practical is through the use of absolute value (which allows
that the difference can be either positive or negative). Using the symbols (delta) and
(epsilon) to represent very small (and possibly unequal) numbers, we can write this
phrase in delta/epsilon form as
if 冟x ⫺ 3冟 6 , then 冟 f 1x2 ⫺ 6冟 6 For now, we’ll simply practice translating similar relationships from words into
symbols, leaving any definitive conclusions for our study of limits in Chapter 12, or a
future study of calculus.
EXAMPLE 3
䊳
Using Delta/Epsilon Form
Use a graphing calculator to explore the value of g1x2 ⫽
x2 ⫹ 3x ⫺ 10
when x is
x⫺2
near 2, then write the relationship in delta/epsilon form.
Solution
䊳
Using a graphing calculator and the approach outlined above produces the tables in
the figures.
From these, it appears that, “if the difference between x and 2 is very small, the
difference between f(x) and 7 is very small.” In delta/epsilon form:
if 冟x ⫺ 2冟 6 , then 冟 f 1x2 ⫺ 7冟 6 .
Now try Exercises 5 through 8
䊳
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Connections to Calculus
At first, modeling this relationship may seem like a minor accomplishment. But
historically and in a practical sense, it is actually a major achievement as it enables us
to “tame the infinite,” since we can now verify that no matter how small ⑀ is, there is a
corresponding ␦ that guarantees
冟 f 1x2 ⫺ 7冟 6 ⑀
whenever
f (x ) is infinitely close to 7
冟x ⫺ 2冟 6 ␦
x is infinitely close to 2
This observation leads directly to the precise definition of a limit, the type of
“limit” referred to in our Introduction to Calculus, found in the Preface (page xxii). As
noted there, such limits will enable us to find a precise formula for the instantaneous
speed of a cue ball as it falls, and a precise formula for the volume of an irregular solid.
Connections to Calculus Exercises
Solve the following equations.
1. To find the length of a rectangle with maximum area
that can be circumscribed by a circle of radius 3 in.
x2
⫽ 0,
requires that we solve 29 ⫺ x2 ⫺
29 ⫺ x2
where the length of the rectangle is 2x. To the
nearest hundredth, what is the length of the
rectangle?
2. To find the height of an isosceles triangle with
maximum area that can be inscribed in a circle of
radius r ⫽ 5 in. requires that we solve
x2
⫺5x
2
⫹
225
⫺
x
⫺
⫽ 0,
225 ⫺ x2
225 ⫺ x2
where the height is 5 ⫹ x. What is the height of the
triangle?
3. If the motion of a particle in turbulent air is
modeled by d ⫽ 1t 12t2 ⫺ 9t ⫹ 182, the velocity
3
1
27 1
of the particle is given by v ⫽ 5t2 ⫺ t2 ⫹ 9t⫺2
2
(d in meters, t in seconds). Find any time(s) t when
velocity v ⫽ 0.
4. In order for a light source to provide maximum
(circular) illumination to a workroom, the light
must be hung at a certain height. While the
complete development requires trigonometry, we
find that maximum illumination is obtained at the
solutions of the equation shown, where h is the
height of the light, k is a constant, and the radius of
illumination is 12 ft. Solve the equation for h by
factoring the least power and simplifying the
3
1
1h2 ⫹ 122 2 2 ⫺ 3h2 1h2 ⫹ 122 2 2
⫽ 0.
result: k
1h2 ⫹ 122 2 3
Use a graphing calculator to explore the value of the function given for values of x near the one indicated. Then write
the relationship in words and in delta/epsilon form.
5. h1x2 ⫽
4x2 ⫺ 9
3
;x⫽
2x ⫺ 3
2
7. w1x2 ⫽
7x3 ⫺ 28x
;x⫽2
x2 ⫺ 4
6. v1x2 ⫽
x3 ⫹ 27
; x ⫽ ⫺3
x⫹3
8. F1x2 ⫽
x2 ⫹ 7x
;x⫽0
x